WCS (Wireless Control System) is a centralised solution for lightweight wireless access points. WCS uses SNMP to communicate with controllers. WCS runs on both Linux and Windows.
There are three versions of WCS:
WCS Base (informs which APs a device is associated with)
WCS Location (can track a device to within less than 10 meters)
WCS Location and 2700 series Wireless Location Appliance (tracking of devices in real-time)
Thursday 17 April 2008
WLAN Management - Ciscoworks WLSE
WLSE is part of the Ciscoworks network management suite for autonomous APs. It's features include:
Configuration: Supports 2500 APs, configurations can be changed on mass
Fault and policy monitoring
Reporting: email, print and export reports
Firmware: centralised firmware upgrades
Radio management: parameter generation, network status and reports
WLSE Administration: logs, security, back and restore, diagnostics, redundancy
Key benefits:
+Improved security - IDS, rogue AP detection etc.
+Simplified AP deployment
+RF visibility
+Dynamic RF Management
+Simplified operations
WLSE requires seperate authenication ACS server, WLSE cut down version includes AAA. WLSE Express is intended for small to medium businesses
WLSE has two modes of setup: Automatic - DHCP, manually using setup scripts and CLI
WLSE Configuration Templates: plug and play deployment, automatic AP configuration, automatic RF configuration, optimal RF configuration. IDS features include automatic shutdown of rogue APs, man in the middle attacks, security policy checks, sensor mode APs.
Configuration: Supports 2500 APs, configurations can be changed on mass
Fault and policy monitoring
Reporting: email, print and export reports
Firmware: centralised firmware upgrades
Radio management: parameter generation, network status and reports
WLSE Administration: logs, security, back and restore, diagnostics, redundancy
Key benefits:
+Improved security - IDS, rogue AP detection etc.
+Simplified AP deployment
+RF visibility
+Dynamic RF Management
+Simplified operations
WLSE requires seperate authenication ACS server, WLSE cut down version includes AAA. WLSE Express is intended for small to medium businesses
WLSE has two modes of setup: Automatic - DHCP, manually using setup scripts and CLI
WLSE Configuration Templates: plug and play deployment, automatic AP configuration, automatic RF configuration, optimal RF configuration. IDS features include automatic shutdown of rogue APs, man in the middle attacks, security policy checks, sensor mode APs.
Wednesday 16 April 2008
WLAN Management - Introduction
There are five elements to Cisco Unified Wireless Networks:
Client Devices - Cisco Compatible Extensions program includes services such as wireless mobility, qos, network management and security
+ 7920 wireless phone, PDA.
Mobility Platform - LWAPs are automatically configured by controllers using LWAPP.
+ Lightweight AP's and bridges
Network Unification - Seamless integration into routing and switching, controllers are repsonsible for IPS and RF management
+ Wireless LAN controllers, 6500 WiSM, ISR and 3750 integration
World-class Network Management - enabling WLANs to be seamless with the rest of the network, making them scaleable and reliable via Wireless Control System (WCS)
+ Features for design, control and monitoring
Unified Advanced Services - Support new mobility applications, wireless VoIP, network admission control, self-defending network, and intrusion detection.
+ Cisco Wireless Location Appliance, WCS, Self-defending Networks, NAC, WiFi phones and RF firewalls
Autonomous Access Points
Configuration on each individual AP, each AP controls it's own RF and mobility functions. Ciscoworks Wireless LAN Solutions Engine can be used to centrally manage the APs. Wireless Domain Services (WDS) provides radio monitoring communication management between the APs and CiscoWorks WLSE.
Lightweight Access Points
Configuration, monitoring and security handled by a centralised WLAN controller. LWAPs depend on controller for control and data transmission. Remote Edge Access Point REAP doesn't require the controller. Cisco WCS can centralise configuration, monitoring and management. WLC can be redundant between WCS groups.
Client Devices - Cisco Compatible Extensions program includes services such as wireless mobility, qos, network management and security
+ 7920 wireless phone, PDA.
Mobility Platform - LWAPs are automatically configured by controllers using LWAPP.
+ Lightweight AP's and bridges
Network Unification - Seamless integration into routing and switching, controllers are repsonsible for IPS and RF management
+ Wireless LAN controllers, 6500 WiSM, ISR and 3750 integration
World-class Network Management - enabling WLANs to be seamless with the rest of the network, making them scaleable and reliable via Wireless Control System (WCS)
+ Features for design, control and monitoring
Unified Advanced Services - Support new mobility applications, wireless VoIP, network admission control, self-defending network, and intrusion detection.
+ Cisco Wireless Location Appliance, WCS, Self-defending Networks, NAC, WiFi phones and RF firewalls
Autonomous Access Points
Configuration on each individual AP, each AP controls it's own RF and mobility functions. Ciscoworks Wireless LAN Solutions Engine can be used to centrally manage the APs. Wireless Domain Services (WDS) provides radio monitoring communication management between the APs and CiscoWorks WLSE.
Lightweight Access Points
Configuration, monitoring and security handled by a centralised WLAN controller. LWAPs depend on controller for control and data transmission. Remote Edge Access Point REAP doesn't require the controller. Cisco WCS can centralise configuration, monitoring and management. WLC can be redundant between WCS groups.
Tuesday 15 April 2008
802.1x, Encryption and Authentication - 802.11i and WPA2
WPA2
+ Support for 802.1x and PSK
+ Similar key distribution and renewal to WPA
+ Supports proactive key caching PKC
+ Supports IDS
IDS is able to detect locate and mitigate rogue devices, manage RF interference, detect snooping, managment frames and hijacking attacks, enforce security configuration policies, perform forensic analysis and compliance reporting.
WPA and WPA2 operate in personal and enterprise modes. Products supporting 802.1x and PSK are enterprise, products supporting PSK only are personal products.
Enterprise WPA= 802.1x/PSK, encryption using TKIP/MIC
Personal WPA2=PSK, encryption using AES-CCMP
Enterprise WPA2=802.1x/EAP encryption using AES-CCMP
Personal WPA=PSK, encryption using TKIP/MIC
+ Support for 802.1x and PSK
+ Similar key distribution and renewal to WPA
+ Supports proactive key caching PKC
+ Supports IDS
IDS is able to detect locate and mitigate rogue devices, manage RF interference, detect snooping, managment frames and hijacking attacks, enforce security configuration policies, perform forensic analysis and compliance reporting.
WPA and WPA2 operate in personal and enterprise modes. Products supporting 802.1x and PSK are enterprise, products supporting PSK only are personal products.
Enterprise WPA= 802.1x/PSK, encryption using TKIP/MIC
Personal WPA2=PSK, encryption using AES-CCMP
Enterprise WPA2=802.1x/EAP encryption using AES-CCMP
Personal WPA=PSK, encryption using TKIP/MIC
802.1x, Encryption and Authentication - WPA, 802.11i and WPA2
WPA is a standards based solution to address vulnerabilities in WEP.
Main features:
Authenticated Key Management - authentication via IEEE 802.1x or PSK
Unicast or broadcast key management - after successful user authentication message integrity and encryption keys are derived, distributed validated and stored on the client and AP
Utilisation of TKIP and MIC - Temporal Key Integrity Protocol (TKIP) and Message Integrity Check (MIC) are elements of the WPA standard.
Initialisation Vector Space Expansion - Per-packet keying via IV hashing and key rotation. IV is expanded from WE 24bits to 48bits.
WPA/802.11i authentication process:
Client and AP exchange initial associated request (probe) and agree security capability. Client authenticated by 802.1x Radius server. When successfully authenticated the server and client will present the same master key (PKM) to the AP. Next a four-way key handshake between client and server takes place, finally a two-way handshake between client and AP takes place a group transient key (GTK) which includes MIC.
Issues of WPA:
- Reliant on RC4
- Hardware may not support WPA
- WPA susceptible to DOS, if two bad MICs occur the BSSID is shutdown for 1 minute
- Dictionary attacks can reveal PSK
Main features:
Authenticated Key Management - authentication via IEEE 802.1x or PSK
Unicast or broadcast key management - after successful user authentication message integrity and encryption keys are derived, distributed validated and stored on the client and AP
Utilisation of TKIP and MIC - Temporal Key Integrity Protocol (TKIP) and Message Integrity Check (MIC) are elements of the WPA standard.
Initialisation Vector Space Expansion - Per-packet keying via IV hashing and key rotation. IV is expanded from WE 24bits to 48bits.
WPA/802.11i authentication process:
Client and AP exchange initial associated request (probe) and agree security capability. Client authenticated by 802.1x Radius server. When successfully authenticated the server and client will present the same master key (PKM) to the AP. Next a four-way key handshake between client and server takes place, finally a two-way handshake between client and AP takes place a group transient key (GTK) which includes MIC.
Issues of WPA:
- Reliant on RC4
- Hardware may not support WPA
- WPA susceptible to DOS, if two bad MICs occur the BSSID is shutdown for 1 minute
- Dictionary attacks can reveal PSK
802.1x, Encryption and Authentication - PEAP
Protected Extensible Authentication Protocol (PEAP), with PEAP only the server requires a certificate, installing a certificate on every client is not required. The RADIUS server must support self-issuing of certificates.
PHASE1 - server-side authentication is performed and an encrypted TLS tunnel is created.
PHASE2 - Client is authenticated using EAP-MSCHAPv2 or EAP-GTC, GTP can use generic databases to authenticate, such as LDAP/NDS, MSCHAP enables MS active directory single sign-on.
Client associates with the AP, only AES traffic is permitted by the AP until RADIUS server authenticates. PEAP goes through phase1/2, the client authenticates the server using the CA to verify the certificate. The client and server establish a secure tunnel, the client submits it's credentials to the server inside the tunnel. The RADIUS server sends a session key in a success packet, the RADIUS server and client negotiate a session encryption key (based on WEP or 802.11i
At the end of the session the client sends an EAPOL logoff packet to the AP, from this point only AES is accepted from the client.
802.1x, Encryption and Authentication - EAP-TLS
Extensible Authentication Protocol - Transport Layer Security (EAP-TLS), TLS the replacement for SSL protocol, using PKI.
Requirements of TLS
1. Client must have a certificate so the network can authenticate it
2. AAA server needs a certificate so the client can authenticate it
3. Certificate Authority (CA) must provide certificates to the client and server
+ Windows single sign-on
+ Supported on Windows platform
Wireless client connects to AP using open authentication, AP only permits AES from client until authenticated by AAA server. Client sends EAPOL start frame to server, AP returns request/identify to client. Client sends it's NAI address to the AP which forwards it to the AAA server, client/server perform mutual authentication using certificate exchange, RADIUS server sends session key in success packet.
RADIUS server and client negotiate session encryption, based on client using WEP or 802.11i. Keys then used for the session. EAPOL logoff packet send from client at end of session, AP returns to only accepting AES.
Requirements of TLS
1. Client must have a certificate so the network can authenticate it
2. AAA server needs a certificate so the client can authenticate it
3. Certificate Authority (CA) must provide certificates to the client and server
+ Windows single sign-on
+ Supported on Windows platform
Wireless client connects to AP using open authentication, AP only permits AES from client until authenticated by AAA server. Client sends EAPOL start frame to server, AP returns request/identify to client. Client sends it's NAI address to the AP which forwards it to the AAA server, client/server perform mutual authentication using certificate exchange, RADIUS server sends session key in success packet.
RADIUS server and client negotiate session encryption, based on client using WEP or 802.11i. Keys then used for the session. EAPOL logoff packet send from client at end of session, AP returns to only accepting AES.
802.1x, Encryption and Authentication - EAP-FAST
Extensible Authentication Protocol - Flexible Authentication via Secure Tunnelling (EAP-FAST) developed by Cisco, submitted to IETF.
+ LEAP uses strong passwords, but LEAP-FAST supports single sign-on for Windows
+ Doesn't use certificates
+ Supported on Windows
+ Full support for 802.1x, AES, 802.11i and TKIP
+ Supports WPA/2 authenticated key management on Win2k/XP
+ Supports roaming and centralised key management CCKM using Wireless Domain Services
+ Supports password expiration/change
PHASE0 (provision PAC) - client dynamically provisioned a Protected Access Credential (PAC) via a secure tunnel
PHASE1 (establish secure tunnel) - Client and AAA server such as ACS authenticate each other and establish secure tunnel
PHASE2 (client authentication) - Client sends it's credentials to the radius server, the radius server authenticates and establishes a client authorisation policy.
A wireless client can only transmit EAP until authenticated by AAA, client sends EAP over LAN (EAPOL) start frame to the AP, the AP sends a request/identify to the client. The client sends it's network identifier NAI to the AP, which the AP sends to the radius server.
The client and server perform mutual authentication (phase 1/2) and the RADIUS server sends a session key to the AP in a success packet. The client/server then negotiate a session key, the client and AP use the key during the session. When the session completes an EAPOL logoff packet is sent to the AP.
+ LEAP uses strong passwords, but LEAP-FAST supports single sign-on for Windows
+ Doesn't use certificates
+ Supported on Windows
+ Full support for 802.1x, AES, 802.11i and TKIP
+ Supports WPA/2 authenticated key management on Win2k/XP
+ Supports roaming and centralised key management CCKM using Wireless Domain Services
+ Supports password expiration/change
PHASE0 (provision PAC) - client dynamically provisioned a Protected Access Credential (PAC) via a secure tunnel
PHASE1 (establish secure tunnel) - Client and AAA server such as ACS authenticate each other and establish secure tunnel
PHASE2 (client authentication) - Client sends it's credentials to the radius server, the radius server authenticates and establishes a client authorisation policy.
A wireless client can only transmit EAP until authenticated by AAA, client sends EAP over LAN (EAPOL) start frame to the AP, the AP sends a request/identify to the client. The client sends it's network identifier NAI to the AP, which the AP sends to the radius server.
The client and server perform mutual authentication (phase 1/2) and the RADIUS server sends a session key to the AP in a success packet. The client/server then negotiate a session key, the client and AP use the key during the session. When the session completes an EAPOL logoff packet is sent to the AP.
Sunday 13 April 2008
802.1x, Encryption and Authentication - Cisco LEAP
Lightweight Extensible Authentication Protocol (LEAP), is an 802.1x authentication type.
+ supported by WiFi WPA/WPA2.
+ Strong mutual authentication between client and RADIUS server
+ Supported on all Cisco products
+ Fast secure roaming between Cisco or Cisco compatible clients at layer 2 and 3
+ Single login with existing userid/password from Microsoft AD
+ Supported on range of OS
Client OS include: MS 98/XP/CE, OS X 9.x/10.x, Linux, DOS
RADIUS servers include: Cisco ACS, Meetinghouse Aegis, Interlink Merit, Funk Odyssey server
Wireless devices include: Cisco WAP/LWAP, WLAN controllers, Cisco unified wireless phone 7920, wireless bridges/repeaters, many Cisco and Cisco compatible WLAN clients
Cisco LEAP process:
1. No traffic permitted except EAP until authenticated
2. AP request/identify message, or start message from client
3. Client responds with userid, which is sent by AP to RADIUS server
4. Radius server authenticates the client via AP
5. Client authenticates the RADIUS server via AP
6. Authentication uses challenge/response, response uses MD5, when authenticated a RADIUS success message is sent to each party.
7. The radius server sends a Pair-wise Master Key (PMK) to the AP, a four-way handshake takes place, then the client can transmit and receive data through a protected session.
+ supported by WiFi WPA/WPA2.
+ Strong mutual authentication between client and RADIUS server
+ Supported on all Cisco products
+ Fast secure roaming between Cisco or Cisco compatible clients at layer 2 and 3
+ Single login with existing userid/password from Microsoft AD
+ Supported on range of OS
Client OS include: MS 98/XP/CE, OS X 9.x/10.x, Linux, DOS
RADIUS servers include: Cisco ACS, Meetinghouse Aegis, Interlink Merit, Funk Odyssey server
Wireless devices include: Cisco WAP/LWAP, WLAN controllers, Cisco unified wireless phone 7920, wireless bridges/repeaters, many Cisco and Cisco compatible WLAN clients
Cisco LEAP process:
1. No traffic permitted except EAP until authenticated
2. AP request/identify message, or start message from client
3. Client responds with userid, which is sent by AP to RADIUS server
4. Radius server authenticates the client via AP
5. Client authenticates the RADIUS server via AP
6. Authentication uses challenge/response, response uses MD5, when authenticated a RADIUS success message is sent to each party.
7. The radius server sends a Pair-wise Master Key (PMK) to the AP, a four-way handshake takes place, then the client can transmit and receive data through a protected session.
802.1x, Encryption and Authentication - 802.1x and EAP
802.1x was originally designed for port based authentication on switches, but has been adapted to enable authentication of wireless clients/WAPs.
+ RADIUS protocol with server can be used to authenticate users, this includes Cisco ACS server
+ Authentication is mutual between the client (supplicant) and server
+ 802.1x can be used with multiple encryption methods such as EAS/WPA/TKIP/WEP
+ Without user intervention 802.1x provides dynamic keys after authentication
+ One time passwords can be used to encrypt plaintext passwords
+ 802.1x supports roaming
+ User management is centralised (better management)
+ RADIUS protocol with server can be used to authenticate users, this includes Cisco ACS server
+ Authentication is mutual between the client (supplicant) and server
+ 802.1x can be used with multiple encryption methods such as EAS/WPA/TKIP/WEP
+ Without user intervention 802.1x provides dynamic keys after authentication
+ One time passwords can be used to encrypt plaintext passwords
+ 802.1x supports roaming
+ User management is centralised (better management)
802.1x, Encryption and Authentication - Evolution of Wireless Security
Fascinating Chapter... :(
WEP (Wired Equivalent Privacy) is a very basic form of wireless security, static key is configured, it's not difficult to capture enough packets to decipher the key. IV (Initial Vector) can be configured to change the key after each packet, but this is not secure either.
- Susceptible to dictionary attacks
- Client doesn't authenticate the AP
LEAP, renamed Cisco Wireless EAP was Cisco's first attempt to improve security on wireless networks, it utilised the following:
+ Server based authentication, utilising 802.1x, passwords/one-time tokens/PKI/machine IDs
+ Dynamic WEP keys (session keys), re-authenticating the user periodically, negotiating a new key (CKIP)
+ Mutual authentication between client and RADIUS server
+ Cisco Message Intergrity Check (CMIC) - detects WEP attacks and replays
WPA - Wifi Alliance Group created interim security method prior to development of 802.11i. WPA utilises the following:
+ Pre-shared Key (PSK), or 802.1x user authentication
+ TKIP (Temporal Key Integrity Protocol, used to create per packet keying, and MIC (message integrity check).
+ Only software upgrade required
WPA2 - utilises AES for encryption and use of IDS to identify and protect from attacks, WPA2 generally requires a hardware upgrade.
WEP (Wired Equivalent Privacy) is a very basic form of wireless security, static key is configured, it's not difficult to capture enough packets to decipher the key. IV (Initial Vector) can be configured to change the key after each packet, but this is not secure either.
- Susceptible to dictionary attacks
- Client doesn't authenticate the AP
LEAP, renamed Cisco Wireless EAP was Cisco's first attempt to improve security on wireless networks, it utilised the following:
+ Server based authentication, utilising 802.1x, passwords/one-time tokens/PKI/machine IDs
+ Dynamic WEP keys (session keys), re-authenticating the user periodically, negotiating a new key (CKIP)
+ Mutual authentication between client and RADIUS server
+ Cisco Message Intergrity Check (CMIC) - detects WEP attacks and replays
WPA - Wifi Alliance Group created interim security method prior to development of 802.11i. WPA utilises the following:
+ Pre-shared Key (PSK), or 802.1x user authentication
+ TKIP (Temporal Key Integrity Protocol, used to create per packet keying, and MIC (message integrity check).
+ Only software upgrade required
WPA2 - utilises AES for encryption and use of IDS to identify and protect from attacks, WPA2 generally requires a hardware upgrade.
Monday 7 April 2008
Wireless LAN QoS - Introduction
Wireless LANs operate in the same mannor as wired LANS at OSI layer 3 and above.
Where wired LANs implement CSMA/CD, wireless LANs (802.11) are not able to detect collisions, so implement collision avoidance - CSMA/CA. Collision Avoidance uses RF carrier sense, random back-off, inter-frame spacing.
802.1e is an approved standard for implementing QoS on wireless networks. Prior to 802.1e being standardised, Wifi Multimedia WMM created a QoS policy based on 4 queues, to prioritise traffic.
WLAN data from a client is sent between the LWAP and controller using LWAPP (Light Weight Access Point Protocol). A LWAP running LWAPP layer 2 will need to be in the same broadcast domain and IP subnet as the controller, however a LWAP in layer 3 mode doesn't have to be in the same IP subnet or broadcast domain. In layer 2 mode the LWAPP protocol is an Ethernet frame, but in layer 3 mode it is a UDP packet.
The following shows the process of QoS continuity is as follows:
1. WLAN controller frame packet marked with 802.q (CoS)
2. WLAN controller encapsulates frame with LWAPP, copies inner DSCP fields to outer LWAPP DSCP field, then maps the DSCP field to the outer CoS field using a mapping table.
3. LWAP forwards the IP packet to the client, it uses the 802.11e layer 2 QoS marking
Where wired LANs implement CSMA/CD, wireless LANs (802.11) are not able to detect collisions, so implement collision avoidance - CSMA/CA. Collision Avoidance uses RF carrier sense, random back-off, inter-frame spacing.
802.1e is an approved standard for implementing QoS on wireless networks. Prior to 802.1e being standardised, Wifi Multimedia WMM created a QoS policy based on 4 queues, to prioritise traffic.
WLAN data from a client is sent between the LWAP and controller using LWAPP (Light Weight Access Point Protocol). A LWAP running LWAPP layer 2 will need to be in the same broadcast domain and IP subnet as the controller, however a LWAP in layer 3 mode doesn't have to be in the same IP subnet or broadcast domain. In layer 2 mode the LWAPP protocol is an Ethernet frame, but in layer 3 mode it is a UDP packet.
The following shows the process of QoS continuity is as follows:
1. WLAN controller frame packet marked with 802.q (CoS)
2. WLAN controller encapsulates frame with LWAPP, copies inner DSCP fields to outer LWAPP DSCP field, then maps the DSCP field to the outer CoS field using a mapping table.
3. LWAP forwards the IP packet to the client, it uses the 802.11e layer 2 QoS marking
Auto QoS
Automated tool for deploying QoS
+Simplifies QoS configuration
+Less chance of configuration error
+Makes deployment simpler, faster and cheaper
+Follows DIVSERV model
Phase 1 - AutoQoS VoIP: designed purely for VoIP, only one command required, supported on majority of switch/router platforms
Pahse 2 - AutoQos Enterprise: Extends to cover VoIP/video/data, only supported on routers
NBAR used for protocol discovery.
Prerequisites:
1. No existing QoS policies on interface
2. CEF enabled on interface
3. Correct bandwidth specified
Enable autoqos enterprise on a router interface: 'auto qos discovery', then 'auto qos'
Enable autoqos voip on switch interface: 'auto qos voip trust' for uplinks (trust markings), 'auto qos voip cisco-phone' (extends trust boundary to phone).
Verify AutoQos on routers:
- show auto discovery qos - auto discovery results
- show auto qos - view templates and initial configuration
- show policy-map interface - shows interface QoS statistics
Verify AutoQoS VoIP on switches:
- show mls qos maps - examine cos to DSCP mappings
Common AutoQoS problems:
1. Too many classes generated - manually consolidate classes
2. QoS configuration doesn't adapt to changing network conditions - re-run discovery
3. QoS configuration doesn't fit specific circumstances - manually configure QoS elements
+Simplifies QoS configuration
+Less chance of configuration error
+Makes deployment simpler, faster and cheaper
+Follows DIVSERV model
Phase 1 - AutoQoS VoIP: designed purely for VoIP, only one command required, supported on majority of switch/router platforms
Pahse 2 - AutoQos Enterprise: Extends to cover VoIP/video/data, only supported on routers
NBAR used for protocol discovery.
Prerequisites:
1. No existing QoS policies on interface
2. CEF enabled on interface
3. Correct bandwidth specified
Enable autoqos enterprise on a router interface: 'auto qos discovery', then 'auto qos'
Enable autoqos voip on switch interface: 'auto qos voip trust' for uplinks (trust markings), 'auto qos voip cisco-phone' (extends trust boundary to phone).
Verify AutoQos on routers:
- show auto discovery qos - auto discovery results
- show auto qos - view templates and initial configuration
- show policy-map interface - shows interface QoS statistics
Verify AutoQoS VoIP on switches:
- show mls qos maps - examine cos to DSCP mappings
Common AutoQoS problems:
1. Too many classes generated - manually consolidate classes
2. QoS configuration doesn't adapt to changing network conditions - re-run discovery
3. QoS configuration doesn't fit specific circumstances - manually configure QoS elements
End-to-end QoS - Control Plane Policing (CoPP)
Packets destined for the control-plane generally include routing protocol control packets, SNMP management traffic, packets destined for the local router's IP address, for example telnet.
It is important to configure QoS for the control-plane in order to prevent DoS attacks that could damage the network infrastructure, for example:
- High CPU utilisation
- Loss of routing updates and keep-alives, resulting in routing-flaps
- Slow response times including access through CLI and VTY lines
- Queue build-ups resulting in packet drops
MQC can be used to define 'trusted' traffic that is allowed un-restricted access to the control-plane, whilst policing all other traffic. QoS policies can be applied to the control-plane in the similar fashion as a router interface.
It is important to configure QoS for the control-plane in order to prevent DoS attacks that could damage the network infrastructure, for example:
- High CPU utilisation
- Loss of routing updates and keep-alives, resulting in routing-flaps
- Slow response times including access through CLI and VTY lines
- Queue build-ups resulting in packet drops
MQC can be used to define 'trusted' traffic that is allowed un-restricted access to the control-plane, whilst policing all other traffic. QoS policies can be applied to the control-plane in the similar fashion as a router interface.
End-to-End QoS - Pre-classify
Pre-classify was designed to classify packets on the output of an interface before data is encrypted and tunnelled. In modern times service providers and customers want to classify traffic within VPN tunnels, providing SLA's to voice/video etc.
VPN aims to provide confidentiality, Authentication and data integrity.
When a packet enters a VPN it's original headers are encapsulated, this means that any QoS on the original headers will not be visible to the QoS mechanisms on the egress interface.
Good news is the old ToS field value is copied to the new headers, however if there is a requirement to classify based on source/destination address, for example, then the 'pre-classify' command need to be used. Pre-classify should be configured on the endpoint prior to the traffic entering the VPN tunnel.
Two common tunneling protocols are IPSEC and GRE, GRE has the advantage of being able to tunnel multicast/broadcast and routing protocol traffic, GRE is not able to provide confidentialilty using encryption.
IPSEC is a more secure protocol, which is able to encrpt only unicast traffic. IPSEC uses two mechanisms to protect data:
Authentication Header (AH) protocol 51: Operates in tunnel mode (adds headers) or transport mode (encapsulates entire packet). Ensures integrity and euthentication of packets.
Encapsulating Security Payload (ESP) protocol 50: Operates in tunnel mode (encrypts only the IP payload), transport mode encrypts the entire original packet.
The pre-classify command takes a duplicate of the original packet to that the service policy is able to examine the packet. This is only required where fields other than TpS need to be inspected (ToS fields are automatically copied from the original packet to the encrypted packet).
Pre-classify can only be configured on tunnel interfaces/virtual templates/crypto-maps.
VPN aims to provide confidentiality, Authentication and data integrity.
When a packet enters a VPN it's original headers are encapsulated, this means that any QoS on the original headers will not be visible to the QoS mechanisms on the egress interface.
Good news is the old ToS field value is copied to the new headers, however if there is a requirement to classify based on source/destination address, for example, then the 'pre-classify' command need to be used. Pre-classify should be configured on the endpoint prior to the traffic entering the VPN tunnel.
Two common tunneling protocols are IPSEC and GRE, GRE has the advantage of being able to tunnel multicast/broadcast and routing protocol traffic, GRE is not able to provide confidentialilty using encryption.
IPSEC is a more secure protocol, which is able to encrpt only unicast traffic. IPSEC uses two mechanisms to protect data:
Authentication Header (AH) protocol 51: Operates in tunnel mode (adds headers) or transport mode (encapsulates entire packet). Ensures integrity and euthentication of packets.
Encapsulating Security Payload (ESP) protocol 50: Operates in tunnel mode (encrypts only the IP payload), transport mode encrypts the entire original packet.
The pre-classify command takes a duplicate of the original packet to that the service policy is able to examine the packet. This is only required where fields other than TpS need to be inspected (ToS fields are automatically copied from the original packet to the encrypted packet).
Pre-classify can only be configured on tunnel interfaces/virtual templates/crypto-maps.
"Where Do I Apply the Service Policy?
You can apply a service policy to either the tunnel interface or to the underlying physical interface. The decision of where to apply the policy depends on the QoS objectives. It also depends on which header you need to use for classification.
-
Apply the policy to the tunnel interface without qos-preclassify when you want to classify packets based on the pre-tunnel header.
-
Apply the policy to the physical interface without qos-preclassify when you want to classify packets based on the post-tunnel header. In addition, apply the policy to the physical interface when you want to shape or police all traffic belonging to a tunnel, and the physical interface supports several tunnels.
-
Apply the policy to a physical interface and enable qos-preclassify when you want to classify packets based on the pre-tunnel header."
Sunday 6 April 2008
Congestion Avoidance - Fragmentation & Interleaving
Provided that the software queue is empty packets go straight to the hardware queue, the hardware queue operates a FIFO policy, the implication of this is that delay sensitive voice packets may be queued behind large packets.
If a typical 1500 byte frame has a be sent on a 256000bits/sec link (256Kb) then a delay of 47ms is created (1500*8/256000).
To reduce the delay created by large queued data units fragmentation and interleaving can be enabled.
If a typical 1500 byte frame has a be sent on a 256000bits/sec link (256Kb) then a delay of 47ms is created (1500*8/256000).
To reduce the delay created by large queued data units fragmentation and interleaving can be enabled.
Congestion Avoidance - Payload & Header Compression
Layer 2 payload compression as the name suggests, compresses frames at layer 2. Payload compression is done on a link by link basis, on protocols such as HDLC/frame-relay/PPP/X.25/LAPB.
The following compression methods are supported on Cisco IOS:
-Stacker
-Predictor
-MPPC (Microsoft Point to Point Compression
Compression does induce an amount of delay, perference is towards hardware based compression, as software/hardware assisted requires more CPU cycles. Layer2 compression of payloads leaves the headers intact as they are required, layer 2 header compression will compress the headers, but leave the payload intact.
Layer 2 header compression sends the first packet in a flow with it's headers, then for all remaining packets in the flow, a hash is calculated and the headers are removed. The receiving router will determine which flow the packet is part of by reviewing the hash value.
The following compression methods are supported on Cisco IOS:
-Stacker
-Predictor
-MPPC (Microsoft Point to Point Compression
Compression does induce an amount of delay, perference is towards hardware based compression, as software/hardware assisted requires more CPU cycles. Layer2 compression of payloads leaves the headers intact as they are required, layer 2 header compression will compress the headers, but leave the payload intact.
Layer 2 header compression sends the first packet in a flow with it's headers, then for all remaining packets in the flow, a hash is calculated and the headers are removed. The receiving router will determine which flow the packet is part of by reviewing the hash value.
Congestion Avoidance - Traffic Policing/Shaping Overview
Traffic Policing aims to limit the traffic rate to less than the physical rate of the interface, limit the traffic rate for particular classes and re-mark traffic.
Traffic Shaping aims to slow down the traffic rate to a value less than the physical rate, often to comply with SLA's. It is also able to shape traffic of different classes to different bit-rates.
- Shaping and policing both measure the traffic rate (sometimes within classes)
- Policing can be applied out and inbound, whereas shaping can only be done outbound.
- Shaping buffers excess packets (requiring extra memory), policing drops or re-marks traffic.
- Only policing can re-mark traffic
- Only traffic shaping can respond to network conditions and signals.
Traffic Shaping aims to slow down the traffic rate to a value less than the physical rate, often to comply with SLA's. It is also able to shape traffic of different classes to different bit-rates.
- Shaping and policing both measure the traffic rate (sometimes within classes)
- Policing can be applied out and inbound, whereas shaping can only be done outbound.
- Shaping buffers excess packets (requiring extra memory), policing drops or re-marks traffic.
- Only policing can re-mark traffic
- Only traffic shaping can respond to network conditions and signals.
Saturday 5 April 2008
Congestion Avoidance - CBWRED
Class-based Weighted Random Early Detection (CBWRED) is a development on WRED which allows profiling of traffic based on class-maps, rather than enabling it at an interface level.
An example configuration of CBWRED:
!
interface FastEthernet 0/0
service-policy output enterprise_policy
!
class-map voice
match ip dscp ef
!
class-map bulk-data
match ip dscp af11
!
policy-map enterprise_policy
class voice
priority 128
class bulk-data
bandwidth 128
random-detect
random-detect dscp af11 22 55 10
class class-default
fair-queue
random-detect
!
show policy-map interface fa0/0 - verify configuration
An example configuration of CBWRED:
!
interface FastEthernet 0/0
service-policy output enterprise_policy
!
class-map voice
match ip dscp ef
!
class-map bulk-data
match ip dscp af11
!
policy-map enterprise_policy
class voice
priority 128
class bulk-data
bandwidth 128
random-detect
random-detect dscp af11 22 55 10
class class-default
fair-queue
random-detect
!
show policy-map interface fa0/0 - verify configuration
Congestion Avoidance - WRED
Weighted Random Early Detection (WRED) works on the same principle as RED, but has the added flexibility of being able to distinguish between high and low priority traffic, identified by DSCP/IPP. This enables WRED to drop more packets of a lower priority to ensure high priority traffic is not affected.
The following shows the configuration required to enable WRED:
interface Hssi0/0/0
description 45Mbps to R1
ip address 10.200.14.250 255.255.255.252
random-detect
random-detect precedence 0 32 256 100
random-detect precedence 1 64 256 100
random-detect precedence 2 96 256 100
random-detect precedence 3 120 256 100
The following shows the configuration required to enable WRED:
interface Hssi0/0/0
description 45Mbps to R1
ip address 10.200.14.250 255.255.255.252
random-detect
random-detect precedence 0 32 256 100
random-detect precedence 1 64 256 100
random-detect precedence 2 96 256 100
random-detect precedence 3 120 256 100
Wednesday 2 April 2008
Congestion Avoidance - Random Early Detection
Random Early Detection (RED) is a mechanism used to prevent tail-drop.
RED drops packets at random before a queue is full, the rate of drops increases as the queue grows. RED is not flow orientated and will drop packets at random without preference. Statistically packets in more aggressive flows will be dropped more frequently.
RED is only effective when the majority of traffic is TCP flows. Because non-TCP flows do not use window sizes they will not benefit from RED.
Three parameters are used to configure RED: low threshold, high threshold and Mark Probability Denominator (MPD). RED will drop one packet of MPD value, for example if MPD was 40, 1 in 40 packets would be dropped.
If the minimum threshold is too low then packets may be dropped too soon, when not necessary. If the maximum threshold is too high when RED will not be able to prevent global syncronisation.
RED drops packets at random before a queue is full, the rate of drops increases as the queue grows. RED is not flow orientated and will drop packets at random without preference. Statistically packets in more aggressive flows will be dropped more frequently.
RED is only effective when the majority of traffic is TCP flows. Because non-TCP flows do not use window sizes they will not benefit from RED.
Three parameters are used to configure RED: low threshold, high threshold and Mark Probability Denominator (MPD). RED will drop one packet of MPD value, for example if MPD was 40, 1 in 40 packets would be dropped.
If the minimum threshold is too low then packets may be dropped too soon, when not necessary. If the maximum threshold is too high when RED will not be able to prevent global syncronisation.
Congestion Avoidance - Tail Drop Limitations
Tail drop occurs when a software queue is unable to hold any more packets arriving. The aim of congestion avoidance is to avoid tail-drop.
Effects of tail-drops include TCP global syncronisation, and TCP starvation
TCP Global Syncronisation occurs when packets from multiple TCP connections are dropped causing the TCP sessions to reduce their window size, once the queue is uncongested the window size is increased again causing tail-drop. Due to the fluctuating window size, and that it affects all TCP sessions it doesn't provide for effective performance.
TCP Starvation occurs then UDP traffic (unaffected by window size fluctuation) fills the queues and prevents TCP packets from entering the queue.
Random Early Detection (RED) is a solution to improve TCP performance
Effects of tail-drops include TCP global syncronisation, and TCP starvation
TCP Global Syncronisation occurs when packets from multiple TCP connections are dropped causing the TCP sessions to reduce their window size, once the queue is uncongested the window size is increased again causing tail-drop. Due to the fluctuating window size, and that it affects all TCP sessions it doesn't provide for effective performance.
TCP Starvation occurs then UDP traffic (unaffected by window size fluctuation) fills the queues and prevents TCP packets from entering the queue.
Random Early Detection (RED) is a solution to improve TCP performance
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