Filtering BGP Updates by Matching the AS_PATH PA

To filter routes by matching the AS_PATH PA, Cisco IOS uses AS_PATH filters. The overall configuration structure is very similar to BGP distribute lists and prefix lists, with the matching logic specified in a list, and the logic being applied with a neighbor command. The main two steps are as follows: 1. Configure the AS_PATH filter using the ip as-path access-list number {permit | deny} regex command. 2. Enable the AS_PATH filter using the neighbor neighbor-id filter-lis..

UDLD and Loop Guard: Protecting Trunks

Both UniDirectional Link Detection (UDLD) and Loop Guard protect a switch trunk port from causing loops. Both features prevent switch ports from errantly moving from a blocking to a forwarding state when a unidirectional link exists in the network. Unidirectional links are simply links for which one of the two transmission paths on the link has failed, but not both. This can happen as a result of miscabling, cutting one fiber cable, unplugging one fiber, GBIC problems..

802.11g

802.11g is backward compatible with 802.11b, which is referred to as 802.11b/g mixed-mode operation. For example, an 802.11b radio card can associate with an 802.11g access point. Most organizations today are deploying 802.11g wireless LANs. Because of its support for data rates up to 54 Mbps, 802.11g offers higher performance than 802.11b systems. Capacity is still somewhat limited, however, because 802.11g operates in the 2.4-GHz band, which limits the number of nonoverlapp..

BGP in the Core

The core is the first place in your network where scaling issues will become apparent. This is because the core tends to combine the largest number of routes with the largest amount of traffic, taxing the routers to their limit. Using BGP in the core allows the routes in the core to separated into two parts: routes within the core and routes external to the core. The iBGP mesh carries the routes external to the core, while the IGP continues to carry just the routes within th..

Using eBGP Multihop

Cisco provides a useful option called eBGP Multihop, which allows you to establish eBGP peer relationships between routers that aren't directly connected to one another: Router1#configure terminal Enter configuration commands, one per line.  End with CNTL/Z. Router1(config)#ip route 172.20.1.2 255.255.255.255 192.168.1.5 2 Router1(config)#router bgp 65500 Router1(config-router)#neighbor 172.20.1.2 remote-as 65530 Router1(config-router)#neighbor 172.20.1.2 update-source ..