Router MAC Address Problem

[Nobleman]

I need some info on this.I have a router/gw with x.x.x.1 Ip address.When a linux system within the same n/w pings the gw, linux box getsupdated with a different MAC address of gw in its ARP table as compared with a Windows system.Both Windows and linux system are in the same network.

However, Windows system is able to use the router effectivity and connect to outside world.I am not able to physically see the router.Neither I am able to use a browser to connect x.x.x.1.

Is the router having 2 or more ethernet adapters but same IP given to each one of them ? How come multiple linux systems are obtaining the MAC address of router whereas windows are obtaining a different set ?

[Marco-D]

I added comp.protocols.tcp-ip to this reply.I don't believe that there is a comp.protocols.arp yet.

It might help if you gave the MAC addresses, or at least the OUI (first six hex digits). Of the possibilities I can think of, one is that they are not really on the same network, but just look that way.(VLAN's being one possibility.) If you exchange the IP addresses, do the MAC addresses follow?

As long as the router accepts data sent to the MAC addresses it returns for ARP, it should work.

Most routers will have one TCP port that they will accept connections on. Traditionally that was 23 (telnet), but more recently 80 (http). Which one did you try ?

It could be some type of load sharing system. Maybe odd addresses to one interface, even to the other, even though both go into the same router and are otherwise on the same subnet.

[Nobleman]

I believe both the linux and windows system are in the same network. linux system receives 00-1c-58 as MAC addr of router whereas windows system receive 00-1f-6c as the router mac address.

I tried port 80.

[Marco-D]

I believe both the linux and windows system are in the same network. linux system receives 00-1c-58 as MAC addr of router whereas windows system receive 00-1f-6c as the router mac address.

I tried port 80.

Both belong to Cisco, if that helps any.

It would seem that they could both be the same router.

[Nobleman]

This is happenening even though I connect Windows and linux system to the same physical port in the same network, During the device discovery phase, linux box uses a different MAC address corresponding to router compared with Windows system. And if I try to manually edit the arp table in linux system, I connect to outside world. I am not sure if the IPv6 stack in linux kernel is causing any issue although I am using using only Ipv4 address.

[Marco-D]

Alternatively you may have run into proxy arp which is on by default on Cisco routers. Under proxy arp a router will send an arp response for an address it can get to (or thinks it can get to) even if not directly connected. This can be a real pain to troubleshoot. Or it may be as you say and both routers have the same IP address.a host should update its arp table with the last info received. That said I may have read it incorrectly - it was only a cursory scan over the info - or the arp handler may choose not to add an entry for the second update. The RFC doesn't look like it was written with this
situation in mind.

So, I guess the answer as to why Windows does one think and Linux the other depends on the software running their arp handling. One thing is for sure. The second router to respond (which is either busier or slower than the first) should not send an arp reply if it cannot reach the address mentioned. I think the next place to look is the router config and see where that leads you.