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SmartSwitch Router User Reference Manual 81
Chapter 6: BGP Configuration Guide
The gated.conf file for router SSR2 is as follows:
IBGP Configuration Example
Connections between BGP speakers within the same AS are referred to as internal links. A
peer in the same AS is an internal peer. Internal BGP is commonly abbreviated IBGP;
external BGP is EBGP.
An AS that has two or more EBGP peers is referred to as a multihomed AS. A multihomed
AS can “transit” traffic between two ASs by advertising to one AS routes that it learned
from the other AS. To successfully provide transit services, all EBGP speakers in the
transit AS must have a consistent view of all of the routes reachable through their AS.
Multihomed transit ASs can use IBGP between EBGP-speaking routers in the AS to
synchronize their routing tables. IBGP requires a full-mesh configuration; all EBGP
speaking routers must have an IBGP peering session with every other EBGP speaking
router in the AS.
An IGP, like OSPF, could possibly be used instead of IBGP to exchange routing
information between EBGP speakers within an AS. However, injecting full Internet routes
(50,000+ routes) into an IGP puts an expensive burden on the IGP routers. Additionally,
IGPs cannot communicate all of the BGP attributes for a given route. It is therefore
recommended that an IGP not be used to propagate full Internet routes between EBGP
speakers. IBGP should be used instead.
IBGP Routing Group Example
An IBGP Routing group uses the routes of an interior protocol to resolve forwarding
addresses. An IBGP Routing group will determine the immediate next hops for routes by
using the next hop received with a route from a peer as a forwarding address, and using
this to look up an immediate next hop in an IGP’s routes. Such groups support distant
peers, but need to be informed of the IGP whose routes they are using to determine
immediate next hops. This implementation comes closest to the IBGP implementation of
other router vendors.
You should use the IBGP Routing group as the mechanism to configure the SSR for IBGP.
If the peers are directly connected, then IBGP using group-type Internal can also be used.
autonomoussystem 2 ;
routerid 10.0.0.2 ;
bgp yes {
group type external peeras 1
{
peer 10.0.0.1
;
};
};