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​BGP - Advertising Routes in IPv4 Unicast

Picture




CSR14
router bgp 100
 address-family ipv4
 network 100.14.14.14 mask 255.255.255.255



CSR15#debug bgp ipv4 unicast update
BGP(0): 100.9.15.9 rcvd UPDATE w/ attr: nexthop 100.9.15.9, origin i, merged path 100, AS_PATH 
BGP(0): 100.9.15.9 rcvd 100.14.14.14/32
BGP(0): Revise route installing 1 of 1 routes for 100.14.14.14/32 -> 100.9.15.9(global) to main IP table
BGP(0): (base) 100.13.15.13 send UPDATE (format) 100.14.14.14/32, next 100.13.15.15, metric 0, path 100
BGP(0): 100.13.15.13 rcvd UPDATE w/ attr: nexthop 100.13.15.13, origin i, merged path 100, AS_PATH 
BGP(0): 100.13.15.13 rcvd 100.14.14.14/32
BGP(0): 100.9.15.9 rcvd UPDATE w/ attr: nexthop 100.9.15.9, origin i, merged path 100, AS_PATH 
BGP(0): 100.9.15.9 rcvd 100.14.14.14/32...duplicate ignored


CSR15#show bgp ipv4 unicast summary 
BGP router identifier 100.15.15.15, local AS number 15
BGP table version is 2, main routing table version 2
1 network entries using 248 bytes of memory
2 path entries using 240 bytes of memory
1/1 BGP path/bestpath attribute entries using 256 bytes of memory
1 BGP AS-PATH entries using 24 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 768 total bytes of memory
BGP activity 1/0 prefixes, 2/0 paths, scan interval 60 secs

Neighbor        V           AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd
100.9.15.9      4          100      55      55        2    0    0 00:46:31        1
100.13.15.13    4          100      41      44        2    0    0 00:37:45        1



CSR15#show bgp ipv4 unicast         
BGP table version is 2, local router ID is 100.15.15.15
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, 
              r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter, 
              x best-external, a additional-path, c RIB-compressed, 
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop            Metric LocPrf Weight Path
 *   100.14.14.14/32  100.13.15.13                           0 100 i
 *>                   100.9.15.9                             0 100 i




CSR15#show bgp ipv4 unicast 100.14.14.14
BGP routing table entry for 100.14.14.14/32, version 2
Paths: (2 available, best #2, table default)
  Advertised to update-groups:
     2         
  Refresh Epoch 1
  100
    100.13.15.13 from 100.13.15.13 (100.13.13.13)
      Origin IGP, localpref 100, valid, external
      rx pathid: 0, tx pathid: 0
  Refresh Epoch 1
  100
    100.9.15.9 from 100.9.15.9 (100.9.9.9)
      Origin IGP, localpref 100, valid, external, best
      rx pathid: 0, tx pathid: 0x0


There are 2 peerings via eBGP to AS 100. But only the peering via IOS9, 100.9.15.9, is the best path. The reason for this is that the IOS9 peering came up first and is the oldest peering therefore it becomes the best path.
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  • Home
  • Technology VoD!
    • Cisco >
      • Route & Switch / Enterprise Infrastructure
  • Technology Breakdowns!
    • Route&Switch/Ent. Infra. >
      • L2 Technologies
      • L3 Technologies
      • VPN Technologies
      • Services >
        • IOS - Dynamic NAT
        • HSRP - IPv4 Setup
        • HSRP - Priority and Preemption
    • Service Provider >
      • IGPs (Interior Gateway Protocols)
      • First Hop Redundancy >
        • HSRP (Hot Standby Router Protocol) >
          • HSRP - IOS/IOS XE Setup
          • HSRP - IOS XR Setup
      • BGP (Border Gateway Protocol)
      • Inter AS Multicast (MSDP)
      • Intra-AS MPLS
      • Inter-AS MPLS
    • Security >
      • IOS Firewall
      • ASA Firewall
      • FirePOWER Threat Defense >
        • FTD - FTD NGFW Device Setup and FMC Integration
      • VPNs >
        • PKI
        • Site to Site VPNs
        • Remote Access VPNs >
          • IOS Remote Access
          • ASA Remote Access
    • Data Center >
      • Nexus 9000v >
        • Nexus 9000v - Enabling Features
        • Nexus 9000v - VLANs and Trunks
        • Nexus 9000v - LACP Port Channels
        • Nexus 9000v - vPC (Virtual Port Channel)
        • Nexus 9000v - OSPFv2
        • Nexus 9000v - VXLAN - Ingress Replication Flood and Learn
        • Nexus 9000v - IP Multicast
        • Nexus 9000v - VxLAN - Multicast Flood and Learn
        • Nexus 9000v - VxLAN - BGP EVPN with Multicast
        • Nexus 9000v - VxLAN - BGP EVPN w/Ingress Replication
        • Nexus 9000v - VxLAN - Inter-VxLAN Routing with BGP EVPN
        • Nexus 9000v - VXLAN - External Routing
      • Nexus 7000v
    • Palo Alto