Tech Library
BGP – Inter-AS Option B
1. Intro BGP Option B is an Inter-AS MPLS L3VPN method in which the ASBRs exchange VPNv4/VPNv6 routes directly using MP-eBGP. It provides better scalability than Option A because the ASBRs do not maintain per-customer VRFs. Find next the our Test Topology : Our aim is to advertise the 192.45.6.1/32 prefix all the way to […]
BGP – Inter-AS Option A
1. Intro BGP Option A is one of the methods for implementing Inter-AS MPLS L3VPNs (VPNs spanning multiple Autonomous Systems). It is the simplest and most isolated of the three common options (A, B, and C). Find next the Test Topology : Our aim is to advertise the 192.45.6.1/32 prefix all the way to R7. […]
BGP – basic multipath
1. Intro BGP typically selects only one best path for each prefix and installs that route in the forwarding table. When BGP multipath is enabled, the device selects multiple equal-cost BGP paths to reach a given destination, and all these paths are installed in the forwarding table. BGP advertises only the active path to its […]
BGP – damping
1. Intro BGP route flapping describes the situation in which BGP systems send an excessive number of update messages to advertise network reachability information. BGP flap damping is a method of reducing the number of update messages sent between BGP peers, thereby reducing the load on these peers, without adversely affecting the route convergence time […]
BGP – IPv6 Peers
In this post we will explore a few variations of an IPv6 BGP neighborship. We will configure an IPv6 eBGP neighborship between two directly connected routers. The routers will advertise to each other the IPv6 loopback addresses. 1. Basic setup A simple basic setup, where we are using the inet6 address that was configured on […]
BGP – AS_TRANS 23456
1. Intro This Post is about the operation of BGP in a network with a mix of 2-byte and 4-byte AS numbers. The 2-byte AS number, also known as a 16-bit AS number, provides a pool of 65,536 AS numbers, which has been exhausted. The 4-byte AS numbers are specified in RFC 4893 and provide […]
BGP – remove-private
1. Intro When advertising AS paths to remote systems, have the local system strip private AS numbers from the AS path. The numbers are stripped from the AS path starting at the left end of the AS path (the end where AS paths have been most recently added). The routing device stops searching for private […]
BGP – as-path-prepend
1. Intro You can prepend one or more autonomous system (AS) numbers at the beginning of an AS path. The AS numbers are added at the beginning of the path after the actual AS number from which the route originates has been added to the path. Prepending an AS path makes a shorter AS path […]
BGP – loops
1. Intro When configured, loops will allow the local device’s AS number to be in the received AS paths, and specify the number of times detection of the local device’s AS number in the AS_PATH attribute causes the route to be discarded. There are 2 ways of configuring loops: As we can see, we can […]
BGP – as-override
1. Intro Compare the AS path of an route with the AS number of the BGP peer in the group, and replace all occurrences of the peer AS number in the AS path with its own AS number before re-advertising the route to the peer. This is essentially an alternate solution to the advertise-peer-as and […]