Cisco IP address conflicts

evo22 · 08-22-2006, 11:41 AM

Hello,

I just configured a new Cisco 1841 Router and attempted to replace our existing router last night and it cause network IP address conflicts with our servers? Sounds like a NAT problem...does anyone know how to fix this issue?

Thanks in advance

Ericunicast · 08-23-2006, 06:48 AM

how was the router configured? staticly or by using a routing protocol, RIP, IGRP etc.?

evo22 · 08-23-2006, 09:03 AM

The router has a static IP and the servers have static IPs. I solved the problem with the conflict. Now I'm having problems with the Firewall, it's only allowing out bound traffic...we host our own website and it will not in coming traffic to our website? I tried IP forwarding no luck.... Any suggestions short of contacting Cisco support?

Thanks in advance...

Ericunicast · 08-23-2006, 09:19 AM

What type of firewall are you using and at what point in the network are you NATing? sounds like another NAT issue.

evo22 · 08-23-2006, 09:26 AM

The Firewall we are using is the built in Cisco 1800 series firewall.

Ericunicast · 08-23-2006, 09:37 AM

The only possible problems i can think of are potential NAT problems. Im stumped for now. Its not an overload because that would eliminate traffic all together. Ill get back to you in a few.

evo22 · 08-23-2006, 09:54 AM

Thanks I appreciate it!

terbolee · 09-05-2006, 05:57 AM

Can I assume you've checked the ACLs to make sure they are working right? On the router, check the existing routing table [show ip route] to make sure that all known routes should be there. An IP address conflict can confuse a router causing it to build an incorrect routing table. You might try clearing the routing table so it can build a new one. I think the command is [clear ip route *] in the Global Configuration mode. Hope this helps.

08-22-2006, 11:41 AM	#1 (permalink)
evo22 Registered User Join Date: Jul 2006 Posts: 13 OS: Windows XP Pro	Cisco IP address conflicts Hello, I just configured a new Cisco 1841 Router and attempted to replace our existing router last night and it cause network IP address conflicts with our servers? Sounds like a NAT problem...does anyone know how to fix this issue? Thanks in advance

08-23-2006, 09:26 AM	#5 (permalink)
evo22 Registered User Join Date: Jul 2006 Posts: 13 OS: Windows XP Pro	The Firewall we are using is the built in Cisco 1800 series firewall. Last edited by evo22; 08-23-2006 at 09:27 AM.

08-23-2006, 06:48 AM	#2 (permalink)
Ericunicast Registered User Join Date: Aug 2006 Posts: 99 OS: win2000	how was the router configured? staticly or by using a routing protocol, RIP, IGRP etc.?

08-23-2006, 09:03 AM	#3 (permalink)
evo22 Registered User Join Date: Jul 2006 Posts: 13 OS: Windows XP Pro	The router has a static IP and the servers have static IPs. I solved the problem with the conflict. Now I'm having problems with the Firewall, it's only allowing out bound traffic...we host our own website and it will not in coming traffic to our website? I tried IP forwarding no luck.... Any suggestions short of contacting Cisco support? Thanks in advance...

08-23-2006, 09:19 AM	#4 (permalink)
Ericunicast Registered User Join Date: Aug 2006 Posts: 99 OS: win2000	What type of firewall are you using and at what point in the network are you NATing? sounds like another NAT issue.

08-23-2006, 09:37 AM	#6 (permalink)
Ericunicast Registered User Join Date: Aug 2006 Posts: 99 OS: win2000	The only possible problems i can think of are potential NAT problems. Im stumped for now. Its not an overload because that would eliminate traffic all together. Ill get back to you in a few.

08-23-2006, 09:54 AM	#7 (permalink)
evo22 Registered User Join Date: Jul 2006 Posts: 13 OS: Windows XP Pro	Thanks I appreciate it!

09-05-2006, 05:57 AM	#8 (permalink)
terbolee Registered User Join Date: Sep 2006 Posts: 25 OS: XP	Can I assume you've checked the ACLs to make sure they are working right? On the router, check the existing routing table [show ip route] to make sure that all known routes should be there. An IP address conflict can confuse a router causing it to build an incorrect routing table. You might try clearing the routing table so it can build a new one. I think the command is [clear ip route *] in the Global Configuration mode. Hope this helps.