>From what I understand the router will not delete the arp entry immediately after it expired so it will not queue/drop the packet Take a look on this output where the arp is expired you the entry is kept without expiration time for few seconds until the other side answer to the arp
nitzan@ROUTER> show arp no-resolve expiration-time | match 10.10.3.58 00:02:ff:10:44:7c 10.10.3.58 ae0.21 none 1 nitzan@ROUTER> show arp no-resolve expiration-time | match 10.10.3.58 00:02:ff:10:44:7c 10.10.3.58 ae0.21 none nitzan@ROUTER> show arp no-resolve expiration-time | match 10.10.3.58 00:02:ff:10:44:7c 10.10.3.58 ae0.21 none 90 Nitzan On Fri, Jan 11, 2019 at 6:51 PM Clarke Morledge <chm...@wm.edu> wrote: > According to KB19396, "the Address Resolution Protocol (ARP) > expiration timer does not refresh even if there is an active traffic flow > in the router. This is the default behavior of all routers running Junos > OS." The default timer is 20 minutes. I have confirmed this behavior on > the MX platform. > > This does not seem very intuitive, as it suggests that a Junos device at > L3 would stop in the middle of an active flow, to send an ARP request to > try to refresh its ARP cache, potentially causing some unnecessary queuing > of traffic, while the Junos device waits for ARP resolution. For an active > flow, the ARP response should come back quick, but still it seems > unnecessary. > > I would have thought that the ARP cache would only start to decrement the > expiration timer, when the device was not seeing any traffic to/from ARP > entry host. > > KB19396 goes onto say, "When the ARP timer reaches 20 (+/- 25%) minutes, > the router will initiate an ARP request for that entry to check that the > host is still alive." I can see that when the ARP timer is started > initially, that it starts the expiration countdown, at this (+/- 25%) > value, and not exactly at, say, 20 minutes, which is the default timer > value. > > A couple of questions: > > (a) Is this default behavior across all Junos platforms, including MX, > SRX, and EX? > > (b) Is there any other caveat as to when the Junos device will send out > the ARP request, at the end of expiration period? > > Clarke Morledge > College of William and Mary > Information Technology - Network Engineering > Jones Hall (Room 18) > 200 Ukrop Way > Williamsburg VA 23187 > _______________________________________________ > juniper-nsp mailing list juniper-nsp@puck.nether.net > https://puck.nether.net/mailman/listinfo/juniper-nsp > _______________________________________________ juniper-nsp mailing list juniper-nsp@puck.nether.net https://puck.nether.net/mailman/listinfo/juniper-nsp
