Service Manual

The AS path is shown in the following example. The origin attribute is shown following the AS path information (shown in bold).
Example of Viewing AS Paths
DellEMC#show ip bgp paths
Total 30655 Paths
Refcount Metric Path
3 18508 701 3549 19421 i
3 18508 701 7018 14990 i
3 18508 209 4637 1221 9249 9249 i
2 18508 701 17302 i
26 18508 209 22291 i
75 18508 209 3356 2529 i
2 18508 209 1239 19265 i
1 18508 701 2914 4713 17935 i
162 18508 209 i
2 18508 701 19878 ?
31 18508 209 18756 i
2 18508 209 7018 15227 i
10 18508 209 3356 13845 i
3 18508 209 701 6347 7781 i
1 18508 701 3561 9116 21350 i
Next Hop
The next hop is the IP address used to reach the advertising router.
For EBGP neighbors, the next-hop address is the IP address of the connection between the neighbors. For IBGP, the EBGP
next-hop address is carried into the local AS. A next hop attribute is set when a BGP speaker advertises itself to another BGP
speaker outside its local AS and when advertising routes within an AS. The next hop attribute also serves as a way to direct
traffic to another BGP speaker, rather than waiting for a speaker to advertise. When a next-hop BGP neighbor is unreachable,
then the connection to that BGP neighbor goes down after hold down timer expiry. The connection flap can also be obtained
immediately with Fallover enabled. BGP routes that contain the next-hop as the neighbor address are not sent to the neighbor.
You can enable this feature using the neighbor sender-side-loopdetect command.
NOTE:
For EBGP neighbors, the next-hop address corresponding to a BGP route is not resolved if the next-hop address is
not the same as the neighbor IP address.
Multiprotocol BGP
MBGP is an extensison of BGP to carry routing information for multiple network-layer protocols such as IPv4 unicast and
multicast, and IPv6 unicast. MBGP provides support for multiple network layer protocol address families that allows to define
independent policy and peering configurations. MBGP carries different set of routes depending on the protocol. It carries routing
information for IPv4 multicast and IPv6 unicast routes. Multiprotocol extensions for BGP (MBGP) is defined in IETF RFC 2858.
MBGP allows different types of address families to be distributed in parallel.
MBGP allows information about the topology of the IP multicast-capable routers to be exchanged separately from the topology
of normal IPv4 and IPv6 unicast routers. It allows a multicast routing topology different from the unicast routing topology.
MBGP uses either an IPv4 address configured on the interface (which is used to establish the IPv6 session) or a stable IPv4
address that is available in the box as the next-hop address. As a result, while advertising an IPv6 network, exchange of IPv4
routes does not lead to martian next-hop message logs.
NOTE:
It is possible to configure BGP peers that exchange both unicast and multicast network layer reachability
information (NLRI), but you cannot connect multiprotocol BGP with BGP. Therefore, you cannot redistribute multiprotocol
BGP routes into BGP.
MBGP for IPv4 Multicast
PIM feature uses IPv4 multicast routing for data distribution. MBGP provides a link that is dedicated specific to multicast traffic.
MBGP also allows a unicast routing apart from the multicast routing. A multicast routing protocol, such as PIM, uses both
the unicast and multicast BGP database to form a routing table for unicast and multicast. You can configure BGP peers that
exchange both unicast and multicast Network Layer Reachability Information (NLRI) in which MBGP routes is redistributed into
BGP. The default is IPv4 unicast.
Border Gateway Protocol (BGP)
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