Design Reference

BGP implementation guidelines
To successfully implement BGP in a VSP 4000 network, follow these guidelines:
• BGP does not operate with an IP router in nonforwarding (host-only) mode. Ensure that the
routers with which you want BGP to operate are in forwarding mode.
• If you use BGP for a multihomed AS (one that contains more than a single exit point), Avaya
recommends that you use OSPF for the IGP, and BGP for the sole exterior gateway protocol.
Otherwise, use intra-AS IBGP routing.
• If OSPF is the IGP, use the default OSPF tag construction. The use of EGP or the modification
of the OSPF tags makes network administration and proper configuration of BGP path
attributes difficult.
• For routers that support both BGP and OSPF, you must configure the OSPF router ID and the
BGP identifier to the same IP address. The BGP router ID automatically uses the OSPF router
ID.
• In configurations where BGP speakers reside on routers that have multiple network
connections over multiple IP interfaces (the typical case for IBGP speakers), consider using the
address of the circuitless (virtual) IP interface as the local peer address. In this configuration,
you ensure that BGP is reachable as long as an active circuit exists on the router.
• By default, BGP speakers do not advertise or inject routes into their IGP. You must configure
route policies to enable route advertisement.
• Coordinate routing policies among all BGP speakers within an AS so that every BGP border
router within an AS constructs the same path attributes for an external path.
• Configure accept and announce policies on all IBGP connections to accept and propagate all
routes. Make consistent routing policy decisions on external BGP connections.
• Use the max-prefix parameter to limit the number of routes BGP imports from a peer. Use a
configuration of 0 to accept an unlimited number of prefixes.
• You cannot enable or disable the MED selection process. BGP aggregation does not occur
when routes have different MEDs or next hops.
BGP and OSPF interaction
RFC1745 defines the interaction between BGP and OSPF when OSPF is the IGP within an
autonomous system. For routers that run both protocols, the OSPF router ID and the BGP ID must
be the same IP address. You must configure a BGP route policy to allow BGP advertisement of
OSPF routes.
Interaction between BGPv4 and OSPF includes the ability to advertise supernets to support CIDR.
BGPv4 supports interdomain supernet advertisements; OSPF can carry supernet advertisements
within a routing domain.
BGP and other vendor interoperability
BGP interoperability is compatible between VSP 4000, Cisco 6500 Software Release IOS 11.3, and
Juniper M20 Software Release 5.3R2.4.
For more information about BGP, see Avaya Virtual Services Platform 4000 Series Configuration —
BGP Services, NN46251-507.
Layer 3 network design
66 Network Design Reference for Avaya VSP 4000 Series December 2014
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