The link between SITE A-C6509B (4/48) and SITE B-C6509A (G3/48) is a 100Mbit/s LAN Extension Service circuit. As a result of problems being experienced with traffic running on this link, a test VLAN was created with ID 2000. This VLAN only exists in these two switches, and only on this one link. The subnet created on this VLAN (172.20.1.0/24) is not included in any routing protocol, and only exists on this VLAN.
172.20.1.2 SITE B-C6509A -> G3/48 -> LES circuit -> G4/48 -> SITE A-C6509B 172.20.1.1
If the link is configured with just VLAN 2000, pinging both ways between the two nodes on 172.20.1.0/24 works fine. It also works if you have VLANs 1 and 2000. However, if you add further VLANs, the following behaviour is exhibited:
An extended ping (10000 packets) from 172.20.1.2 (on SITE B-C6509A) to 172.20.1.1 (on SITE A-C6509B) fails. However, the ARP table is completed correctly for 172.20.1.2. Also, the mac address table is showing the mac address for 172.20.1.2 in VLAN2000 correctly via G3/48. The same is true at the other end of the link - the arp and mac tables for 172.20.1.2 are completed correctly. After a while, the mac address table times out at both ends, even with the continued ping attempts.
Whilst the extended ping is failing, issuing "ping 172.20.1.2" from SITE A-C6509B not only works, but it causes a few hundred pings in the opposite direction to succeed.
OSPF is the routing protocol