09-09-2021 07:26 AM - edited 09-09-2021 07:28 AM
Just testing out simple iBGP with 2 routers using a loopback address each. Before peering the loopback addresses and configuring "update-source", the loopback interfaces are able to ping each other using iBGP. After peering the loopback addresses, the link keeps flapping.
- show ip route does show the route to each loopback address
- show ip bgp topo * also show the network as "valid" and "best"
Any idea why it is flapping up and down?
*Sep 9 22:14:26.963: %BGP-3-NOTIFICATION: sent to neighbor 1.1.1.1 4/0 (hold time expired) 0 bytes SG01-RT02(config-router)# *Sep 9 22:14:26.967: %BGP-5-NBR_RESET: Neighbor 1.1.1.1 reset (BGP Notification sent) *Sep 9 22:14:26.975: %BGP-5-ADJCHANGE: neighbor 1.1.1.1 Down BGP Notification sent *Sep 9 22:14:26.979: %BGP_SESSION-5-ADJCHANGE: neighbor 1.1.1.1 IPv4 Unicast topology base removed from session BGP Notification sent *Sep 9 22:14:27.151: %BGP-5-ADJCHANGE: neighbor 1.1.1.1 Up SG01-RT02(config-router)# *Sep 9 22:17:38.467: %BGP-3-NOTIFICATION: sent to neighbor 1.1.1.1 4/0 (hold time expired) 0 bytes SG01-RT02(config-router)# *Sep 9 22:17:38.471: %BGP-5-NBR_RESET: Neighbor 1.1.1.1 reset (BGP Notification sent) *Sep 9 22:17:38.475: %BGP-5-ADJCHANGE: neighbor 1.1.1.1 Down BGP Notification sent *Sep 9 22:17:38.475: %BGP_SESSION-5-ADJCHANGE: neighbor 1.1.1.1 IPv4 Unicast topology base removed from session BGP Notification sent *Sep 9 22:17:38.671: %BGP-5-ADJCHANGE: neighbor 1.1.1.1 Up
Below are the "show run".
Thanks.
SG01-RT01#sh run Building configuration... Current configuration : 2238 bytes ! ! Last configuration change at 19:52:03 UTC Thu Sep 9 2021 ! version 15.2 service timestamps debug datetime msec service timestamps log datetime msec ! hostname SG01-RT01 ! boot-start-marker boot-end-marker ! ! ! no aaa new-model no ip icmp rate-limit unreachable ip cef ! ! ! ! ! ! no ip domain lookup no ipv6 cef ! ! multilink bundle-name authenticated ! ! ! ! ! ! ! ! ! ip tcp synwait-time 5 ! ! ! ! ! ! ! ! ! ! ! ! interface Loopback1 ip address 1.1.1.1 255.255.255.0 ! interface Ethernet0/0 no ip address shutdown duplex auto ! interface GigabitEthernet0/0 no ip address shutdown media-type gbic speed 1000 duplex full negotiation auto ! interface FastEthernet1/0 no ip address shutdown speed auto duplex auto ! interface FastEthernet1/1 no ip address shutdown speed auto duplex auto ! interface FastEthernet2/0 no ip address shutdown speed auto duplex auto ! interface FastEthernet2/1 no ip address shutdown speed auto duplex auto ! interface FastEthernet3/0 ip address 192.168.1.1 255.255.255.0 speed auto duplex auto ! interface FastEthernet3/1 no ip address shutdown speed auto duplex auto ! interface Serial4/0 no ip address shutdown serial restart-delay 0 ! interface Serial4/1 no ip address shutdown serial restart-delay 0 ! interface Serial4/2 no ip address shutdown serial restart-delay 0 ! interface Serial4/3 no ip address shutdown serial restart-delay 0 ! interface FastEthernet5/0 no ip address shutdown speed auto duplex auto ! interface FastEthernet5/1 no ip address shutdown speed auto duplex auto ! interface FastEthernet6/0 no ip address shutdown speed auto duplex auto ! interface FastEthernet6/1 no ip address shutdown speed auto duplex auto ! router bgp 65200 bgp log-neighbor-changes network 1.1.1.0 mask 255.255.255.0 network 192.168.1.0 neighbor 1.2.0.1 remote-as 65200 neighbor 1.2.0.1 update-source Loopback1 neighbor 192.168.1.2 remote-as 65200 ! ip forward-protocol nd ! ! no ip http server no ip http secure-server ! ! ! ! control-plane ! ! line con 0 exec-timeout 0 0 privilege level 15 logging synchronous stopbits 1 line aux 0 exec-timeout 0 0 privilege level 15 logging synchronous stopbits 1 line vty 0 4 login ! ! end
SG01-RT02#sh run Building configuration... *Sep 9 22:24:00.431: %BGP-3-NOTIFICATION: sent to neighbor 1.1.1.1 4/0 (hold time expired) 0 bytes Current configuration : 1802 bytes ! ! Last configuration change at 22:19:56 UTC Thu Sep 9 2021 ! version 15.2 service timestamps debug datetime msec service timestamps log datetime msec ! hostname SG01-RT02 ! boot-start-marker boot-end-marker ! ! ! no aaa new-model no ip icmp rate-limit unreachable ip cef ! ! ! ! --More-- *Sep 9 22:24:00.435: %BGP-5-NBR_RESET: Neighbor 1.1.1.1 reset (BGP Notification sent) *Sep 9 22:24:00.443: %BGP-5-ADJCHANGE: neighbor 1.1.1.1 Down BGP Notification sent *Sep 9 22:24:00.447: %BGP_SESSION-5-ADJCHANGE: neighbor 1.1.1.1 IPv4 Unicast topology base removed from session BGP Notification sent *Sep 9 22:24:00.647: %BGP-5-ADJCHANGE: neighbor 1.1.1.1 Up ! ! no ip domain lookup no ipv6 cef ! ! multilink bundle-name authenticated ! ! ! ! ! ! ! ! ! ip tcp synwait-time 5 ! ! ! ! ! ! ! ! ! ! ! ! interface Loopback1 ip address 1.2.0.1 255.255.255.255 ! interface Ethernet0/0 no ip address shutdown duplex auto ! interface GigabitEthernet0/0 no ip address shutdown media-type gbic speed 1000 duplex full negotiation auto ! interface FastEthernet1/0 no ip address shutdown speed auto duplex auto ! interface FastEthernet1/1 no ip address shutdown speed auto duplex auto ! interface FastEthernet2/0 no ip address shutdown speed auto duplex auto ! interface FastEthernet2/1 no ip address shutdown speed auto duplex auto ! interface FastEthernet3/0 no ip address shutdown speed auto duplex auto ! interface FastEthernet3/1 no ip address shutdown speed auto duplex auto ! interface FastEthernet4/0 ip address 192.168.1.2 255.255.255.0 speed auto duplex auto ! interface FastEthernet4/1 no ip address shutdown speed auto duplex auto ! router bgp 65200 bgp log-neighbor-changes network 1.2.0.1 mask 255.255.255.255 network 192.168.1.0 neighbor 1.1.1.1 remote-as 65200 neighbor 1.1.1.1 update-source Loopback1 neighbor 192.168.1.1 remote-as 65200 ! ip forward-protocol nd ! ! no ip http server no ip http secure-server ! ! ! ! control-plane ! ! line con 0 exec-timeout 0 0 privilege level 15 logging synchronous stopbits 1 line aux 0 exec-timeout 0 0 privilege level 15 logging synchronous stopbits 1 line vty 0 4 login ! ! end
09-09-2021 12:42 PM - edited 09-09-2021 12:46 PM
BGP often needs or runs over the IGP like OSPF, EIGRP, etc (static routes will do too). I do not see any of those, so you have a case when BGP puts route(s) into RIB but BGP itself needs those route(s) to reach other guy. Think about BGP as a TCP/IP application protocol not as protocol itself. You can run BGP over directly connected interface w/o any other protocols (try it) but once you use loopbacks to establish BGP, it needs help. Add static routes telling us how to reach other guy's loopback and let us know if that helped.
Regards, ML
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09-09-2021 01:24 PM
Thanks. I'd seen examples on the Internet of how static route and other IGPs are used and was wondering why I couldn't find any using iBGP as THE IGP so I thought I'd give it a try. Was wondering if it's some misconfiguration or some command I'd missed, since I actually could use iBGP and ping between the loopbacks. Problem only starts when i tried to form neighborship between the 2 loopback interfaces.
So I guess it's really not possible at all. Thanks!
09-09-2021 03:58 PM
Just noticed that you do have extra commands! you have 2 peerings: 1 directly and 1 via loopback, check it using show ip bgp status, which one is UP and not going down? you need only neighbor statement; BGP is slow but big; it is not recommended as IGP although could work. Note that BGP keep alive time out is 180 seconds.
neighbor 1.1.1.1 remote-as 65200 .. neighbor 192.168.1.1 remote-as 65200
Regards, ML
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