DHCP client is unable to ping adjacent VLAN

[calvin.chan]

DHCP client is connected to user access with dual uplink to two different 6509 cores. HSRP is also enabled on both 6509 in which VLANs is preempted to two 6509 alternatively.

Sometime, a DHCP client obtain IP via a DHCP server located in server VLAN farm. The user is able to ping all client within the same subnet, its gateway and all 6509 vlan interfaces.

The current 6509 MSFC image is "c6msfc2-jsv-mz.121-12c.E5.bin" while supervisor engine image is "cat6000-sup2k8.7-3-2.bin"

Please help. This condition happens from time to time and automatically heal one day later.

[bflowers]

Sounds like a routing issue. Try adding this command:

ip route 0.0.0.0 0.0.0.0 vlan1 - or whichever vlan it is.

[calvin.chan]

But, only a particular IP within a subnet has this problem. All the remaining IP of the same subnet are working fine. Hence, the problem is quite specific to a particular IP in this day while the other particular IP in another day. There is no pattern we can conclude in this stage.

[rjackson]

Sounds like the DHCP server is reusing an address before the router's arp cache has aged out. You can ping the gateway and that updates your gateway routers cache but the other vlan is using the other router that still has the mac of the last host that had that address. Next time it happens try pinging both routers with their real IP addresses (not the HSRP address) from the problem client. Then try pinging the other vlan. You could also try clear ARP cache on both routers.

If that fixes it try making your DHCP server hold used addresses longer or make the router age its arp entries faster (I dont know how to do either).