This article discusses a specific scenario we've encountered. It details an issue where a customer faced a connection failure while attempting to ping remote destinations, receiving the message "connect: No route to host" despite having the correct routes listed in the route table.
The root cause of this issue was traced back to incorrect configurations. I encourage you to review the symptoms and solution section for a detailed understanding of the problem and how to resolve it.
labuser@labrouter> ping X00X:X998:f00:1::1
Mar 27 04:00:04
connect: No route to host
labuser@labrouter> show route X00X:X998:f00:1::1
Mar 27 04:15:32
inet6.0: 7649 destinations, 25920 routes (7499 active, 0 holddown, 604 hidden)
Restart Complete
+ = Active Route, - = Last Active, * = Both
X00X:X998:f00:1::1/128
*[BGP/170] 6w0d 19:07:03, localpref 150, from X60X:X000::5:4c
AS path: XXXXX XXXXX ?, validation-state: unverified
> to X60X:X000:0:4:100::1c via ae1.0
labuser@labrouter> show route forwarding-table destination X00X:X998:f00:1::1
Mar 27 04:08:28
Routing table: default.inet6
Internet6:
Destination Type RtRef Next hop Type Index NhRef Netif
X00X:X998:f00:1::1/128 user 0 indr 57637 1
sftw 321623 1 ae1.0
rjct 601305 1 ae1.0
We have narrowed it down to an incorrect IPv6 subnet configuration on AE1.
Our analysis shows that the recursive route lookup for the destination address was pointing to the local subnet configured on AE1. However, since the far end of the local router is not configured for this subnet, the IPv6 Neighbor Discovery Protocol (NDP) for the subnet was not completed.
labuser@labrouter> show route X00X:X998:f00:1::1 extensive
Mar 27 04:23:53
X00X:X998:f00:1::1/128 (4 entries, 1 announced)
TSI:
KRT in-kernel X00X:X998:f00:1::1/128 -> {indirect(57637)}
*BGP Preference: 170/-151
Next hop type: Indirect, Next hop index: 0
Address: 0xe52a79c
Next-hop reference count: 15
Source: X60X:X000::5:4c
Next hop type: Router, Next hop index: 321623
Next hop: X60X:X000:0:4:100::1c via ae1.0, selected
Session Id: 237a7
Protocol next hop: X60X:X000:0:4:100::1c
Indirect next hop: 0x59c8688 57637 INH Session ID: 145315
State: <Active Int Ext>
Local AS: XXXXX Peer AS: XXXXX
Age: 6w0d 19:15:25 Metric2: 0
Validation State: unverified
Task: BGP_10796.X60X:X000::5:4c
Announcement bits (2): 0-KRT 7-Resolve tree 6
AS path: XXXXX XXXXX ? (Originator)
...
labuser@labrouter> show route X60X:X000:0:4:100::1c
Mar 27 04:24:14
X60X:X000:0:4::/64 *[Direct/0] 6w0d 19:15:46
> via ae1.0
labuser@labrouter> show configuration interfaces ae1
Mar 27 04:24:30
unit 0 {
family inet6 {
address X60X:X000:0:4::5:3f5/64;
address X60X:X07:X110:bd::2/64;
}
labuser@labrouter> show ipv6 neighbors interface ae1.0
Mar 27 04:25:03
IPv6 Address Linklayer Address State Exp Rtr Secure Interface
X60X:X000:0:4::1:15 00:00:00:00:00:00 unreachable 4 yes no ae1.0
X60X:X000:0:4::1:17 00:00:00:00:00:00 unreachable 4 yes no ae1.0
X60X:X000:0:4:100::11 00:00:00:00:00:00 unreachable 4 yes no ae1.0
X60X:X000:0:4:100::1c 00:00:00:00:00:00 unreachable 4 yes no ae1.0
labuser@labrouter# show | compare
Mar 27 04:41:41
[edit interfaces ae1 unit 0 family inet6]
- address X60X:X000:0:4::5:3f5/64;
Mar 27 04:44:05
PING X00X:X998:f00:1::1(X00X:X998:f00:1::1) 56 data bytes
64 bytes from X00X:X998:f00:1::1: icmp_seq=1 ttl=60 time=17.0 ms
64 bytes from X00X:X998:f00:1::1: icmp_seq=2 ttl=60 time=17.0 ms
64 bytes from X00X:X998:f00:1::1: icmp_seq=3 ttl=60 time=16.9 ms
64 bytes from X00X:X998:f00:1::1: icmp_seq=4 ttl=60 time=16.9 ms
64 bytes from X00X:X998:f00:1::1: icmp_seq=5 ttl=60 time=16.8 ms