{"id":3522,"date":"2012-02-08T16:28:39","date_gmt":"2012-02-08T16:28:39","guid":{"rendered":"http:\/\/www.wikisee.info\/?p=3522"},"modified":"2016-08-09T12:07:30","modified_gmt":"2016-08-09T12:07:30","slug":"bgp-support-for-fast-peering-session-deactivation","status":"publish","type":"post","link":"https:\/\/wiki-see.info\/wp\/2012\/02\/08\/bgp-support-for-fast-peering-session-deactivation\/","title":{"rendered":"BGP Support for Fast Peering Session Deactivation"},"content":{"rendered":"


\nThe BGP<\/span> Support for Fast Peering Session Deactivation feature introduces an event driven notification <\/span>
\nsystem that allows a Border Gateway Protocol (BGP<\/span>) process to monitor BGP<\/span> peering sessions on a <\/span>
\nper-neighbor basis. <\/span><\/p>\n

This feature improves the response time of BGP<\/span> to adjacency changes by allowing :<\/span><\/p>\n

BGP<\/span> to detect an adjacency change and deactivate the terminated session in between standard <\/span>
\nBGP<\/span> scanning intervals. Enabling this feature improves overall BGP convergence<\/span>.<\/span><\/p>\n

Restrictions for BGP Support for Fast Peering Session Deactivation :<\/span><\/span><\/p>\n

\u2022 This feature is not supported under the IPv6 address family.<\/span>
\n\u2022 A host route must be available for each peering session that is configured to use BGP fast session <\/span>
\ndeactivation. If a route is aggregated or is an unreachable non-host route (through a loopback interface) <\/span>
\nbut still available to the peer, this feature will not be able to track the route and will be unable to close the session.<\/span><\/p>\n

Information About BGP Support for Fast Peering Session Deactivation<\/span><\/p>\n

\u2022BGP Hold Timer<\/span>
\n\u2022BGP Fast Peering Session Deactivation<\/span><\/p>\n

BGP Hold Timer<\/span><\/p>\n

By default, the<\/span> BGP<\/span> hold timer is set to run every 180 seconds in Cisco IOS software. <\/span>
\nThis timer value is set as default to protect the<\/span> BGP<\/span> routing process from instability that can be <\/span>
\nintroduced by peering sessions with other routing protocols<\/span>. BGP<\/span> routers typically carry large routing tables, <\/span>
\nso frequent session resets are not desirable.<\/span><\/p>\n

BGP Fast Peering Session Deactivation<\/span><\/p>\n

BGP<\/span> fast peering session deactivation improves BGP convergence and response time to adjacency
\nchanges with BGP neighbors. This feature is event driven and configured on a per-neighbor basis.
\nWhen this feature is enabled, BGP<\/span> will monitor the peering session with the specified neighbor.
\nAdjacency changes are detected and terminated peering sessions are deactivated in between the default
\nor configured BGP scanning interval.<\/span><\/p>\n

How to Configure Fast Peering Session Deactivation<\/span><\/p>\n

This section contains the following task<\/span>:<\/p>\n

\u2022Configuring Fast Session Deactivation for a BGP Neighbor<\/span><\/p>\n

The<\/span> neighbor fall-over<\/span><\/em> command was introduced to support BGP fast session deactivation.<\/span><\/p>\n

SHUT DOWN BGP SESSION BASED ON TRACKED OBJECT<\/span><\/p>\n

I used a creative approach to create a static route that fits the requirements of the
\nFast Peering Deactivation: <\/span><\/span>a host route toward the BGP<\/span> next hop pointing at BGP<\/span> <\/span>next hop.<\/span><\/p>\n

Let\u2019s walk through a lab-tested example:<\/span><\/p>\n

The router is running<\/span> BGP<\/span> in<\/span> AS#65100<\/span> and has an<\/span> EBGP<\/span> session with 10.0.7.10 in<\/span> AS#65000<\/span>:<\/p>\n

router bgp 65100<\/span>
\nbgp log-neighbor-changes<\/span>
\n network 10.0.1.1 mask 255.255.255.255<\/span>
\n neighbor 10.0.7.10 remote-as 65000<\/span><\/p>\n

First we have to create the track object that will cause the<\/span> BGP<\/span><\/span> session termination. It can track<\/span>
\nanything \u2013\u00a0you can track interface state, use<\/span> IP SLA<\/span> and ping the firewall,<\/span>\u00a0or even use EEM to<\/span>
\n<\/span>trigger time-based \u00a0(or other event-based) session shutdown.\u00a0I decided to track the state of the LAN interface.<\/span>
\n!<\/span>
\ntrack 10 interface FastEthernet0\/0 ip routing<\/span>
\n carrier-delay<\/span><\/p>\n

Next, create a host route for the<\/span> BGP<\/span> <\/span>next hop pointing to the next hop itself<\/span>.
\nIf you use a PPP interface to connect to the BGP next hop, make sure you disable<\/span>
\npeer neighbor-route<\/span><\/span>, otherwise the router creates a competing host route for th<\/span>e BGP<\/span><\/span> next hop.<\/span><\/p>\n

ip route 10.0.7.10 255.255.255.255 Serial1\/0 10.0.7.10<\/span> track 10<\/span><\/span>
\n!<\/span>
\ninterface Serial1\/0<\/span>
\n description Link to AS65000<\/span>
\n ip address 10.0.7.9 255.255.255.252<\/span>
\n encapsulation ppp<\/span>
\nno peer neighbor-route<\/span><\/p>\n

We need a prefix-list and a route-map to match the host route toward the BGP<\/span> next hop:<\/span><\/p>\n

ip prefix-list BGP_OK<\/span> seq 5 permit 10.0.7.10\/32<\/span>
\n!<\/span>
\nroute-map BGP_OK<\/span> permit 10<\/span>
\n match ip address prefix-list BGP_OK
\n<\/span><\/span>!<\/span>
\nAnd finally, we can configure the fast BGP<\/span> session deactivation on the EBGP<\/span> session:<\/span><\/p>\n

router bgp 65100<\/span><\/span>
\nneighbor 10.0.7.10 fall-over route-map<\/span> BGP_OK<\/span><\/p>\n

Test#1<\/span> \u2013 shut down the LAN interface. BGP<\/span> session is shut down almost immediately<\/span>
\n(you can fine-tune the delay with track object parameters).<\/span><\/p>\n

A1#conf t<\/span><\/em>
\nEnter configuration commands, one per line. End with CNTL\/Z.<\/span><\/em>
\nA1(config)#int fa 0\/0<\/span><\/em>
\nA1(config-if)#shut<\/span><\/em>
\nA1(config-if)#<\/span><\/em>
\n15:27:55.719: %LINK-5-CHANGED: Interface FastEthernet0\/0, changed state to <\/span><\/em>
\n administratively down<\/span><\/em>
\n15:27:56.383: %TRACKING-5-STATE: 10 interface Fa0\/0 ip routing Up->Down<\/span><\/em>
\n15:27:56.415: %BGP-5-ADJCHANGE: neighbor 10.0.7.10 Down Route to peer lost<\/span><\/em>
\n15:27:56.415: %BGP_SESSION-5-ADJCHANGE: neighbor 10.0.7.10 IPv4 Unicast <\/span><\/em>
\n topology base removed from session Route to peer lost<\/span><\/em>
\n15:27:56.719: %LINEPROTO-5-UPDOWN: Line protocol on Interface <\/span><\/em>
\n FastEthernet0\/0, changed state to down<\/span><\/em><\/p>\n

Test#2<\/span> \u2013 re-enable the LAN interface. BGP<\/span> session is reestablished in less than a second. Perfect \ud83d\ude09<\/span><\/p>\n

A1(config-if)#no shut<\/span><\/em>
\nA1(config-if)#<\/span><\/em>
\n15:29:22.211: %LINK-3-UPDOWN: Interface FastEthernet0\/0, changed state to up<\/span><\/em>
\n15:29:22.395: %TRACKING-5-STATE: 10 interface Fa0\/0 ip routing Down->Up<\/span><\/em>
\n15:29:22.511: %BGP-5-ADJCHANGE: neighbor 10.0.7.10 Up<\/span><\/em>
\n15:29:23.211: %LINEPROTO-5-UPDOWN: Line protocol on Interface<\/span><\/em>
\n FastEthernet0\/0, changed state to up<\/span><\/em><\/p>\n

 <\/p>\n

In Summary<\/span> :<\/p>\n

router bgp 65100<\/span>
\nbgp log-neighbor-changes<\/span>
\nnetwork 10.0.1.1 mask 255.255.255.255<\/span>
\nneighbor 10.0.7.10 remote-as 65000<\/span><\/span>
\n!<\/span>
\n\u00a0track 10<\/span> interface FastEthernet0\/0 ip routing<\/span>
\ncarrier-delay<\/span>
\n!<\/span>
\nip route 10.0.7.10 255.255.255.255 Serial1\/0 10.0.7.10<\/span>\u00a0track 10
\n<\/span>!
\ninterface Serial1\/0<\/span>
\nno peer neighbor-route<\/span>
\n!\u00a0<\/span>
\n\u00a0ip prefix-list\u00a0BGP_OK<\/span>\u00a0seq 5 permit 10.0.7.10\/32<\/span>
\n!
\nroute-map\u00a0BGP_OK<\/span>\u00a0permit 10<\/span>
\nmatch ip address prefix-list\u00a0BGP_OK<\/span><\/span>
\n!<\/span>
\nrouter bgp 65100<\/span>
\nneighbor 10.0.7.10 fall-over route-map\u00a0BGP_OK<\/span><\/span><\/p>\n","protected":false},"excerpt":{"rendered":"

The BGP Support for Fast Peering Session Deactivation feature introduces an event driven notification system that allows a Border Gateway Protocol (BGP) process to monitor BGP peering sessions on a per-neighbor basis. This feature improves the response time of BGP to adjacency changes by allowing : BGP to detect an adjacency change and deactivate the […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[16],"tags":[124],"class_list":["post-3522","post","type-post","status-publish","format-standard","hentry","category-bgp-2","tag-bgp-fast-peering-session"],"_links":{"self":[{"href":"https:\/\/wiki-see.info\/wp\/wp-json\/wp\/v2\/posts\/3522","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/wiki-see.info\/wp\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wiki-see.info\/wp\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wiki-see.info\/wp\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/wiki-see.info\/wp\/wp-json\/wp\/v2\/comments?post=3522"}],"version-history":[{"count":1,"href":"https:\/\/wiki-see.info\/wp\/wp-json\/wp\/v2\/posts\/3522\/revisions"}],"predecessor-version":[{"id":4981,"href":"https:\/\/wiki-see.info\/wp\/wp-json\/wp\/v2\/posts\/3522\/revisions\/4981"}],"wp:attachment":[{"href":"https:\/\/wiki-see.info\/wp\/wp-json\/wp\/v2\/media?parent=3522"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wiki-see.info\/wp\/wp-json\/wp\/v2\/categories?post=3522"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wiki-see.info\/wp\/wp-json\/wp\/v2\/tags?post=3522"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}