A routing loop occurs after an AR2240 summarizes routes. The following figure shows the networking.
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In the figure, Router2 connects to the carrier network (Internet) through an EBGP connection. OSPF runs between two AR2240s (Router1 and Router2) and two ME60s. Router2 summarizes routes to the network segment 192.168.128.160/30 using the ip route-static 192.168.128.160 255.255.255.248 Null 0 command and re-advertises the summarized static route into OSPF.
Run the display ip routing-table command to check the IP routing table of Router2.
<Huawei> display ip routing-table
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Routing Tables: Public
Destinations : 9 Routes : 9
Destination/Mask Proto Pre Cost Flags NextHop Interface
192.168.128.160/29 Static 60 0 D 0.0.0.0 NULL0
192.168.128.160/29 OSPF 10 2 D 192.168.128.158 GigabitEthernet2/0/0
……
The IP routing table shows that the path of traffic from Router2 to 192.168.128.161 is Router2--ME60B--ME60A. In this situation, Router2 can ping 192.168.128.161 successfully.
<Huawei> ping 192.168.128.161
PING 192.168.128.161: 56 data bytes, press CTRL_C to break
Reply from 192.168.128.161: bytes=56 Sequence=1 ttl=255 time=4 ms
Reply from 192.168.128.161: bytes=56 Sequence=2 ttl=255 time=2 ms
Reply from 192.168.128.161: bytes=56 Sequence=3 ttl=255 time=3 ms
Reply from 192.168.128.161: bytes=56 Sequence=4 ttl=255 time=2 ms
Reply from 192.168.128.161: bytes=56 Sequence=5 ttl=255 time=2 ms
--- 192.168.128.161 ping statistics ---
5 packet(s) transmitted
5 packet(s) received
0.00% packet loss
round-trip min/avg/max = 2/2/4 ms
Run the tracert command to tracert 192.168.128.161.
<Huawei>tracert 192.168.128.161
traceroute to 192.168.128.161(192.168.128.161), max hops: 30 ,packet length: 4
0,press CTRL_C to break
1 192.168.128.158 9 ms 3 ms 4 ms
2 192.168.128.161 9 ms 3 ms 4 ms
After the OSPF cost of GE2/0/0 on Router2 is changed to 10, the IP routing table of Router2 is changed:
<Huawei> display ip routing-table
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Routing Tables: Public
Destinations : 9 Routes : 9
Destination/Mask Proto Pre Cost Flags NextHop Interface
192.168.128.160/29 Static 60 0 D 0.0.0.0 NULL0
192.168.128.160/29 OSPF 10 3 D 192.168.128.138 GigabitEthernet3/0/0
……
The IP routing table shows that the path of traffic from Router2 to 192.168.128.161 becomes Router2--Router1--ME60A. In this situation, Router2 cannot ping 192.168.128.161.
Run the tracert command to tracert 192.168.128.161.
<Huawei> tracert 192.168.128.161
traceroute to 192.168.128.161(192.168.128.161), max hops: 30 ,packet length: 4
0,press CTRL_C to break
1 192.168.128.138 9 ms 3 ms 4 ms
2 192.168.128.137 9 ms 3 ms 4 ms
3 192.168.128.138 9 ms 3 ms 4 ms
4 192.168.128.137 9 ms 3 ms 4 ms
5 192.168.128.138 9 ms 3 ms 4 ms
6 192.168.128.137 9 ms 3 ms 4 ms
The tracert result shows that packets remain transmitted between Router1 and Router2 without being forwarded to the destination. However, Router1 can ping 192.168.128.161 successfully.
