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Connectivity problems with Cisco routers and switches

 
 
Oliver Habegger
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      02-18-2005
Hi news group

I am not a Cisco specialist and I am just looking for a feedback for a
problem we are facing at our ISP infrastructure.

We got two ISPs and they are doing BGP together. This was now checked
various times and is obviously not the problem.

The symthoms are, from one of this router we cannot ping a certain internal
IP address, but from the other we can. Between the ISP routers and the
firewall cluster we have Catalyst 2950-12 Switch.

when I plugin a PC directly to this switch, we have no problem at all
reaching everything without interruption. But comming from the Internet,
certain IP are reachable for 30 seconds then down for another 30 seconds and
reachable again. Toggeling the whole day up and down.

Now what I have seen on the Cisco switch is the following:

interface FastEthernet0/1
description router2
switchport access vlan 200
switchport mode access
speed 100
duplex full

interface FastEthernet0/2
description router1
switchport access vlan 200
speed 100
duplex full

And router 1 is the one having problem reaching certain internal IPs. Has it
something to do with the line "switchport mode access" which is missing
there?

Thanks and bye,
Oliver



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Merv
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      02-18-2005
post the complete configs for both routers and the 2950 switch

 
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Oliver Habegger
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      02-18-2005
> post the complete configs for both routers and the 2950 switch
Sorry I got no access and the routers, so I don't know what the
configuration is.

For the switch I could provide more infos if you tell me what exactly you
need! Except passwords and IPs of course )

Bye, Oliver



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Merv
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      02-18-2005
you should definitely have "switch mode access" configured on both
switch ports that are connected to your routers

 
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Merv
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      02-18-2005
so who is running the ping tests to the internal IP address ? Your
ISPs?

If you can ping the Internal IP address from the switch but not via the
routers, then you also need to look at the firewall config to see what
it accepts or blocks with repsect to ICMP echo anbd echo-reply.

Set up a monitoring port on your switch and then capture the ICMP
traffic using something like Etherreal while the ping tests are
conducted from the router that does not work - do you see an inbound
ICMP echo from the router?

put a sniifer on the inside segment to see if that ICMP echo makes it
thru the firewall

 
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Oliver Habegger
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      02-18-2005
> so who is running the ping tests to the internal IP address ? Your
> ISPs?

The ISP did the tests from the routers and repported be that from one router
the IPs are not reachable. I presonally can do the test from the Internat
and see the ping toggeling up and down. So I guess this is because once it
runs through router 1 and 20 seconds later through router 2. This is what i
feel, but I guess this does not really help, does it?

> If you can ping the Internal IP address from the switch but not via the
> routers, then you also need to look at the firewall config to see what
> it accepts or blocks with repsect to ICMP echo anbd echo-reply.

No, block everything is opne fpr ICMP at this time. And as I mentions from a
PC connected to this switch it works ok.

> put a sniifer on the inside segment to see if that ICMP echo makes it
> thru the firewall

This is the next stept we have planned to do, I just though I will ask here
first so I get some ideas what it could be.

> you should definitely have "switch mode access" configured on both
> switch ports that are connected to your routers

Ok, this already helps me, as this is not configured on the port which leads
to the router having a problem. We are going to change this first!

Thanks and bye,
Oliver



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