Here is the fix I propose :
Fix : Check the adjacency is with the same router as the source of the hellos.
In this case, it is not the same, as adjacency with previous router R1
prevails while hellos are arriving from newly connected router R2. Hence, bring
down the adjacency with previous router R1, so the next hello from newly
connected router R2 will be processed and a new adjacency will be created with
the R2. This can be done by checking the source of the hello received once an
adjacency is up, if a mismatch is detected, kill the adjacency and let the next
hellos trigger creating the new adjacency.
Here is the patch. I am comparing the source of hello with the adjacency id.
To bring down the adjacency, I simply call isis_adj_state_change (adj,
ISIS_ADJ_DOWN, "adj do not exist anymore")
In our case, this will invoke isis_delete_adj which takes care of the SPF
recalculation.
isis_pdu.c: check for source ID on receiving hello, match adjacency with source
of hellos
If an adjacency exists, check the adjacency is with the
same router as the source of the hellos. In case a mismatch
is detected, bring down the adjacency and let the next
hello trigger creating the new adjacency.
Files:
Modified isisd/isis_pdu.c
--- a/isisd/isis_pdu.c
+++ b/isisd/isis_pdu.c
@@ -566,6 +566,14 @@ process_p2p_hello (struct isis_circuit *circuit)
* the circuit
*/
adj = circuit->u.p2p.neighbor;
+ /* If an adjacency exists, check it is with the source of the hello packets
*/
+ if (adj){
+ if (memcmp(hdr->source_id, adj->sysid, ISIS_SYS_ID_LEN)){
+ zlog_debug("hello source and adjacency do not match, set adj
down\n");
+ isis_adj_state_change (adj, ISIS_ADJ_DOWN, "adj do not exist
anymore");
+ return 0;
+ }
+ }
if (!adj || adj->level != hdr->circuit_t)
{
if (!adj)
Please review and comment.
Thanks,
Amritha
From: Nambiar, Amritha [mailto:[email protected]]
Sent: Thursday, January 22, 2015 12:43 PM
To: [email protected]
Subject: [quagga-dev 11967] isisd : Adjacency update issue
Adjacency is not formed with the new router when swapping routers on mesh
connections within hello expiry interval.
When a router R1 is disconnected from router R0 and replaced with a link to
another router R2 on the same port of R0 within the hello expiry interval, the
router R1 (that was disconnected) is still seen in the topology. R0 fails to
form adjacency with the new router R2.
Root cause : When the router R1 was disconnected from R0, the adjacency with
R1 continues to exist until its hello/adjacency expiry interval times out. When
router R2 was swapped into R0 on the same port (as R1 once occupied) within the
time the hellos from previously connected R1 expired, an adjacency is already
up and existing (with a non-existent R1). Even though hellos from R2 arrive at
R0, these hellos are never checked for their source and consequently processed
to update the adjacency, while the previous adjacency with a non-existent R1
prevails as the hold time does not expire since new hellos continue to arrive.
Has anyone seen this issue before ?
Thanks,
Amritha
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