08-04-2010 12:26 PM - edited 03-04-2019 09:18 AM
I have an 891 router and I am configuring a static default pointing out one of the WAN links. The problem is, specifying a next hop of the wan interface (Fa8 in this case) does not work. However, specifying a next hop of DHCP works perfectly.
ip route 0.0.0.0 0.0.0.0 fastethernet8 (no work)
ip route 0.0.0.0 0.0.0.0 dhcp (works)
Why would this be?
Thanks,
-J
Solved! Go to Solution.
08-04-2010 03:30 PM
I think the reason for the default route statement with a physical interface not working is that the upstream router is not sending any proxy-arp for the ip addresses you are requesting arp for.
In simple words, If you set up a default route to physical interface and you are trying to reach 4.2.2.2 , your router will look into its routing table and will not find any route for it other than a default route pointing to Fethernet 8, so it will think that 4.2.2.2 is directly connected to it from that interface and will try ARP for 4.2.2.2 , having not recieve anything than from the upstream router ( which is not sending any proxy-arp ) it will just drop it as it will not be able to make a frame for that address 4.2.2.2.
hope i am making any sense here
Manish
08-04-2010 02:35 PM
Your configuration guide is here:
The guide says:
ip route prefix mask {ip-address | interface-type interface-number [ip-address]}
Try doing:
ip route 0.0.0.0 0.0.0.0 fastethernet 8
That should work.
Cheers, rate if this helps!
Tim
08-04-2010 02:56 PM
Yep Yep... that's exactly what I did. It doesn't work if you specify a next hop of a physical interface. It takes the command, shows the command in the config, but won't route.
-J
08-04-2010 03:04 PM
And FA8 is set as a non-switchport, right?
08-04-2010 03:06 PM
sure is... it's one of the two wan ports on the router. The 891 has two WAN interfaces. Fa8 and Gig0.
-J
08-04-2010 03:11 PM
By next hop of physical interface , you mean the exit interface of the router right ?
manish
08-04-2010 03:14 PM
Yes, that is correct, Fa8 is the exit interface on the router. The 891 has switchports Fa0-7 and wan interfaces fast 8 and gig 0.
-J
08-04-2010 03:30 PM
I think the reason for the default route statement with a physical interface not working is that the upstream router is not sending any proxy-arp for the ip addresses you are requesting arp for.
In simple words, If you set up a default route to physical interface and you are trying to reach 4.2.2.2 , your router will look into its routing table and will not find any route for it other than a default route pointing to Fethernet 8, so it will think that 4.2.2.2 is directly connected to it from that interface and will try ARP for 4.2.2.2 , having not recieve anything than from the upstream router ( which is not sending any proxy-arp ) it will just drop it as it will not be able to make a frame for that address 4.2.2.2.
hope i am making any sense here
Manish
08-04-2010 03:49 PM
ahhhh... you may be correct here. There is a no proxy-arp set on the dhcp gateway address. I will need to test this tomorrow am (as it's a production net) thanks for the tip, I'll let you know how it works.
-J
08-05-2010 07:37 AM
yep, that was the problem. Removing proxy-arp solved it.
-J
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