I examine the ping in a test config in the packet tracer. The config:
PC1 - Switch - (Fa0/1) RouterA (Fa0/0) - (Fa0/0) RouterB (Fa0/1) - PC2
I configured the routers default gateway as follows:
RouterA : ip router 0.0.0.0 0.0.0.0 fastethernet 0/0
RouterB : ip router 0.0.0.0 0.0.0.0 fastethernet 0/0
I pinged the PC1 from PC2, but the ping is dropped at the routerB, in the process when it wanted to create the output pdu at layer2.
When I changed the default gateway style as
on routerA : ip router 0.0.0.0 0.0.0.0 18.104.22.168
on routerB : ip router 0.0.0.0 0.0.0.0 22.214.171.124
where routerA Fa0/0 ip address is 126.96.36.199 and routerB Fa0/0 ip is 188.8.131.52
I think in the first case the process can't get the ip address of the gateway so there is no gateway mac address for the layer 2 frame. While in the second case the gateway exact ip address is known.
My question is: if am I right, in what situation is the "ip route <addr> <mask> <interface>" format used for?
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I addition to what Dongbo wrote, it is generally not a good thing to configure the default route using only the physical interface as a next hop is this interface is a broadcast interface. In more recent IOS versions, we issue the following warning message if you do so.
R1(config-if)#ip route 0.0.0.0 0.0.0.0 e1/0
%Default route without gateway, if not a point-to-point interface, may impact performance
Ohh I see,
Because in the p2p environment there is only 2 participant, so it is obvious which interface on the segment is the gateway.
as far as i can see in packet tracer there is no proxy arp
thank you for your help
have a nice day
Hope your doing well,Please go through this documet "Static Routes With Next Hop As An Exit Interface Or An IP Address".It may help you.
Community Manager - NI
I have just read it
"2) If you configured static route point to outgoing interface, forwarding router assume destination address is directly connected to that interface and router will try to find the L2 address of the destination by sending ARP request out of the interface to the destination address in case of Ethernet or looking for a static/dynamic map entry in the mapping table in case of frame-relay."
So if I undersatnd it well, this kind of routing can't be work without proxy arp in the other side, because the router think that every forwarding traffic destination is the on its outgoing interface segment, and try to find its MAC address with an apr request on that outgoing interface. Hmm.
The page you linked said in this scenario (with proxy arp enabled) there will be a large amount of arp request and a larger arp table in that router. So I think it should be usable in an environment where the router (on which the default gateway given with the interface format) doesn't have to forward to a lot of different destination. Or is it a wrong hypothesis? Is there environment where this is useful?
It is recommended to use next hop as ip address than interface for multi-access interface like Ethernet, Frame-relay point to multipoint interfaces .let's assume if you configure default route on internet router pointing interface next-hop to interface no than ip address, So for every destination you will have an arp entry in table ,you can think how many arp entries will be there .Adding ARP for Ethernet /or static L2 mapping in case of FR will be just a workaround in lab topology .I just Provided info for user better understanding. Hope that clears to you, Let me know if you have anything in your mind
Technical Community Manager -NI