Overlapping IP Addresses in interfaces

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Nov 13th, 2009
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Hi ,


I need to configure two public IP on Cisco 1841 ( both on same subnet), 1st IP is on Dailer interface to internet and 2nd IP is on Fa0/0 which is connected back to Sonicwall Firewall.


When I confiure 2nd IP on C1841 Fa0/0 , I gets error message saying 'Overlapss with Dialer0'.


I need to assign 2nd addrress on C1841 fa0/0 becasue its connected to Sonciwall which will also have a public IP address in the same subnet.


How can I confiure public IP on Soniwall. I have 6 public IP available , only one is used for Dialer0 inteface.


Sonnicwall be doing NATing and VPNing.Sonicwall should be visible/pingable from internet using its public IP.



Can you please advise.


Many thanks

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Reza Sharifi Fri, 11/13/2009 - 14:54
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Hi Salman,


You can not assign the same IP subnet to 2 different interfaces. Since you have 6 available IPs that equals to a /29 subnet, so you can make 2 /30s out of your /29 and then assign one /30 per interface.


HTH

Reza




s.nasheet Fri, 11/13/2009 - 15:14
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Reza,


Thanks. But if I change it to /30 mask ,then Dailer0 interface may not communciate with the my ISP/Internet as its currently sits on 255.255.255.248 subnet, if I change to to 255.255.255.252 then will I beak the internet connectivity ?


Do my ISP need to change anything from there end to make this configuration working?


Can I simply assign /32 mask on Dialer interfacce and /30 mask reserve /30 mask for sonicwall and C1841 fa0/0.


Thanks for helping.

s.nasheet Fri, 11/13/2009 - 15:33
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Can I configure C1841 fa0/0 with 95.141.153.233/29 and configure Dialer0 with IP unnumbered Fa0/0.


Can anyone please advise.


Thanks

s.nasheet Fri, 11/13/2009 - 15:37
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Can I configure C1841 fa0/0 with 95.141.153.233/29 and configure Dialer0 with IP unnumbered Fa0/0.


Can anyone please advise.


Thanks

Reza Sharifi Fri, 11/13/2009 - 19:26
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Salman,


Is this an ADSL connection to your service provider? If this is the case, can you use "ip address negotiated" under interface dialer and let the provider take care of that? You usually don't assign IP to a dialer interface.


HTH

Reza


s.nasheet Sun, 11/15/2009 - 09:42
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Hi Reza,


This is SDSL connection to my ISP. I understand I can use IP address negotiated command under dailer interface but my problem is I need to assign 2nd public IP on the router' Fa0/0 interface( on same subnet) to communicate with the Sonicwall using public IP.


So something like below.


C1841-> two interfaces


Dailer 0 connected to interface ,

Ip unnumbered fastethernet0/0

Fa0/0 IP address 213.142.25.10/29 which is connecting back to sonicwall using 213.142.25.10



I Just need to establish layer 3 connecticity using public IP but problem is I can't configure routers fa0/0 with public IP if dailer interface already has a IP address on the same range.


PLease advise I need to re-design network,


Thanks



Paolo Bevilacqua Sun, 11/15/2009 - 11:31
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If you are given a single subnet, you gotta use unnumbered onn dialer.

s.nasheet Sun, 11/15/2009 - 14:32
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Yes mate , it is just a single subnet with /29 mask.

If I confiure dailer interface with ip unnumbered fastethernet0/0 with it defenitly for ?

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