Hi,

I've setup a Linux router which is the gateway for
some of my VLANs (vlan group1). Next hop is a cisco gigabit switch
which is also the router for some other VLANs (vlan group2).
Cisco's ARP cache holds all the IPs of the pcs in vlan group2
but not the IPs of vlan group1 (behing the linux).

I know that this is normal to happen, but I would like
to share/forward the linux's ARP cache to the cisco switch
in order for Ciscoworks to be able to locate
the pc's behind the Linux router.

regards,

Giannis

hi zal1en,

Sorry, but I've never heard of sharing arp caches between devices, or that it is a requirement for CW. The last time I used CiscoWorks the discovery process used higher layer protocols like icmp, snmp etc could you please confirm ?

thanks,

kbp

I've never heard of arp sharing either...
I think you're right that CW works on higher layer protocols.

Here is the problem:

Suppose I have only a 1 Cisco router and I want
to locate the physical location of a pc.
CW queries (I guess with snmp) the router
and finds the MAC address of the pc which resides
in the router's ARP cache. CW then queries
the switches for this MAC address and locates
the switch and the port that the pc is connected.

When I have the linux router the ARP of the pc
stays on the linux. The router does not know
the MAC address of that IP so I cannot
locate the switch/port the pc is connected.

So I thought that maybe there is way from linux
to tell the cisco router,
'hi here is my arp table, copy it to yours'.

But I guess this is scifi cause it's another network layer...

I'll check if CW can ask via snmp the Linux router
to find the arp table.

thanks for answering

Giannis

Hi zal1en,

I think you're on the right track but you missed a point. If we say your network looks like this:

[pc]--[cisco_switch1]--[linux_router]--[cisco_switch2]--[cisco_router]--?
|------ network_1 ----------| |-------------network_2 --------| |--- net_3 ?

then there will be at least 2 networks.

Using the pc as an example - you will never see arp entries on [pc] for [cisco_switch2] which is on [network_2], once [pc] determines that the destination is not local, it will send the traffic to [linux_router].

example arp table on [pc]:

cisco_switch1 aa:bb:cc:dd:ee:ff
linux_router dd:ee:ff:aa:bb:cc

CiscoWorks will scan all the networks via icmp to find devices, it will then attempt to determine the types of those devices and extract information from them. The discovery of which switch and port number [pc] is connected to will happen because CW will find [cisco_switch1] on the network and query it directly for information. The only reason CW may not find information for [pc] would be if you had a firewall enabled, if for example iptables was running on [linux_router] then it might block icmp,snmp,telnet,ssh between networks

Sorry if that was a bit long and rambling but I hope it helps,

cheers,

kbp

That is not the case. I have iptables in linux but the switches
are managed from a different network/VLAN, accessible by CW.
If CW knew pc's MAC address it would be able to find info about [pc].
CW will not find info about [pc] because CW will not be
able to find it's MAC address. The MAC address which belongs
to [pc]'s IP address will be known only to linux.
[switch1] will know the MAC address but will not know
the [pc]'s IP address.
That's the problem I'm trying to solve :-/

So maybe the right question would be:
Can I load linux snmp MIBs on CW? But probably this
is not the place/forum to ask such a question...

cheers

Giannis