this is due to the nature of a BVI interface. it's a "virtual" interface.
so if all the physical links associated with it are brought down, we
bring the BVI down. when there is at least one physical link that
is up, we will bring the BVI up. since the BVI is a virtual interface
and has no fixed mac address, we compute a MAC address each time it
comes up. end stations may not pick up the gratuitous arp we send out
when an interface comes up, so they may not see the new MAC address for
the BVI interface (it is likely to be different each time as we add some
randomness to the algorithm). to avoid this issue, configure a static
mac address on the BVI interface and the problem will be avoided. the
reason why in the earlier (no static mac address) a ping fixes the issue
is because the router is going to arp for the end device (we would have
flushed our arp cache when the interface went down), so both devices
would now have the correct arp entries for each other.
regards
.siva
>
>
> Just some weird behaviour i've noticed from a device, dunno if its my
> setup, or something else i'm doing wrong.
>
> I have a BVI setup over an ATM circuit. When the ATM circuit goes down,
> the router breaks down the BVI group as well, and when the circuit comes
> back up, it rebuilds the BVI and all is well again. However, the client
> must ping the router, or the router must ping the client to reset the
> ARP.. if the client tries to pass any data THROUGH the router, the router
> refuses to update the ARP table and let the traffic flow. Only a ping
> to/from the router fixes the problem?
>
> On Thu, 1 Feb 2001, Siva Valliappan wrote:
>
> | by default, when we arp for a device it remains in our arp cache for
> | 4 hours. 1 minute before the entry expires, we will re-arp for the device.
> | if it responds, we reset the age. if it does not respond, we expire the
> | entry. should (during the 4 hour period) the device send out a
> | gratuitous arp, or arp for the router, we will reset the age interval
> | (since the device is obviously alive). we will not reset the age interval
> | for data traffic (if we did, we would have to keep constantly resetting
> | the age interval)
> |
> | cheers
> | .siva
>
> --
> John Gonzalez / johng@netmdc.com / johng@tularosa.net
> Tularosa Communications, Inc. (505) 439-0200 voice / (505) 443-1228 fax
> http://www.tularosa.net / ASN 11711 / JG6416
> [----------------------------------------------[ sys info ]-----------]
> 12:30pm up 147 days, 18:59, 5 users, load average: 0.23, 0.21, 0.18
>
This archive was generated by hypermail 2b29 : Sun Aug 04 2002 - 04:12:27 EDT