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serpant2012
 Post subject: classfull routing table
PostPosted: Mon Aug 06, 2012 4:23 pm 
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I have a quick question, in a class-full routing table, does this packet get dropped or gets forwarded to the static?

R 172.16.30.0/24 variably subnetted
C 172.16.0.0/24
C 172.16.0.0/25
C 192.168.10.0 is directly connected FA0/0
S* 0.0.0.0/0
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Reggle
PostPosted: Mon Aug 06, 2012 5:30 pm 
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What packet?
Also, overlapping routes in the routing table? Not likely.

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errtime
PostPosted: Wed Aug 08, 2012 12:15 pm 
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Reggle wrote:
Also, overlapping routes in the routing table? Not likely.

It's perfectly valid- the most specific route wins.


Last edited by errtime on Wed Aug 08, 2012 12:22 pm, edited 1 time in total.

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jdsilva
PostPosted: Wed Aug 08, 2012 12:18 pm 
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Not certification related. Moving to Routing and Switching.

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Reggle
PostPosted: Wed Aug 08, 2012 1:55 pm 
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errtime wrote:
Reggle wrote:
Also, overlapping routes in the routing table? Not likely.

It's perfectly valid- the most specific route wins.

Woops, yes. Brainfart.

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totaluser
PostPosted: Wed Aug 08, 2012 2:18 pm 
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the question might be how to force a routing table to be classful

I tried with some recent 12.4T IOS and even though no ip classless was specified, default route was used
CCNP ROUTE FLG states that they tested is with some 12.2 IOS on Cisco 2500 router (pretty prehistoric stuff) and it behaved classfully with no ip classless
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Kaiga
PostPosted: Wed Aug 08, 2012 2:57 pm 
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I mean, you could just lower the AD of the route you need it to use over the classless route?
Or in this case, use RIPv1 or IGRP?

I'd say no, the packet wouldn't be dropped, as stated, the packet would just be sent via the more specific route. (It would be pushed to the /25 instead of the /24)

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Reggle
PostPosted: Wed Aug 08, 2012 5:02 pm 
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errtime wrote:
Reggle wrote:
Also, overlapping routes in the routing table? Not likely.

It's perfectly valid- the most specific route wins.

Again I'm going to insist: not possible. The two routes are shown as 'C' - Connected. IOS would give an error message. Having overlapping routes from static or routing protocols would be fine though.

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errtime
PostPosted: Thu Aug 09, 2012 12:04 am 
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Reggle wrote:
errtime wrote:
Reggle wrote:
Also, overlapping routes in the routing table? Not likely.

It's perfectly valid- the most specific route wins.

Again I'm going to insist: not possible. The two routes are shown as 'C' - Connected. IOS would give an error message. Having overlapping routes from static or routing protocols would be fine though.

Maybe the IOS you've tried it indeed gives an error but in general Cisco IOS accepts such configuration. Few times been using this configuration when client needed to migrate to/from smaller/bigger subnet.
The only thing IOS does not allow is to configure both subnets with the same IP address- then it gives an error message. As long as the IP addresses are unique, you are fine.
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Reggle
PostPosted: Thu Aug 09, 2012 3:18 am 
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Code:
SW3#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
SW3(config)#int vlan10
SW3(config-if)#ip addr
*Mar  1 13:11:09.328: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan10, changed stat               
SW3(config-if)#ip addr 172.16.0.1 255.255.255.0
SW3(config-if)#exi
SW3(config)#int vlan20
SW3(config-if)#ip addr
*Mar  1 13:11:41.196: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan20, changed sta               
SW3(config-if)#ip addr 172.16.0.2 255.255.255.128
172.16.0.0 overlaps with Vlan10
SW3(config-if)#end
SW3#show ver
*Mar  1 13:12:15.912: %SYS-5-CONFIG_I: Configured from console by consoleer
Cisco IOS Software, C3550 Software (C3550-IPSERVICESK9-M), Version 12.2(44)SE6, RELEASE SOFTWARE (fc1)

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mellowd
PostPosted: Thu Aug 09, 2012 3:19 am 
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You can do overlapping subnets with serial links

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errtime
PostPosted: Thu Aug 09, 2012 4:02 am 
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Reggle wrote:
Code:
SW3#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
SW3(config)#int vlan10
SW3(config-if)#ip addr
*Mar  1 13:11:09.328: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan10, changed stat               
SW3(config-if)#ip addr 172.16.0.1 255.255.255.0
SW3(config-if)#exi
SW3(config)#int vlan20
SW3(config-if)#ip addr
*Mar  1 13:11:41.196: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan20, changed sta               
SW3(config-if)#ip addr 172.16.0.2 255.255.255.128
172.16.0.0 overlaps with Vlan10
SW3(config-if)#end
SW3#show ver
*Mar  1 13:12:15.912: %SYS-5-CONFIG_I: Configured from console by consoleer
Cisco IOS Software, C3550 Software (C3550-IPSERVICESK9-M), Version 12.2(44)SE6, RELEASE SOFTWARE (fc1)

Try it under the same L3 interface with one of the subnets as a secondary.
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Reggle
PostPosted: Thu Aug 09, 2012 5:55 am 
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errtime wrote:
Try it under the same L3 interface with one of the subnets as a secondary.

Hey, I learned something today! Thanks!

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Asalehipour
PostPosted: Thu Aug 09, 2012 12:37 pm 
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errtime wrote:
Reggle wrote:
Code:
SW3#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
SW3(config)#int vlan10
SW3(config-if)#ip addr
*Mar  1 13:11:09.328: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan10, changed stat               
SW3(config-if)#ip addr 172.16.0.1 255.255.255.0
SW3(config-if)#exi
SW3(config)#int vlan20
SW3(config-if)#ip addr
*Mar  1 13:11:41.196: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan20, changed sta               
SW3(config-if)#ip addr 172.16.0.2 255.255.255.128
172.16.0.0 overlaps with Vlan10
SW3(config-if)#end
SW3#show ver
*Mar  1 13:12:15.912: %SYS-5-CONFIG_I: Configured from console by consoleer
Cisco IOS Software, C3550 Software (C3550-IPSERVICESK9-M), Version 12.2(44)SE6, RELEASE SOFTWARE (fc1)

Try it under the same L3 interface with one of the subnets as a secondary.

what does that mean ? can u explain more ?
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errtime
PostPosted: Fri Aug 10, 2012 1:06 am 
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you can configure multiple subnets under the interface with one of them being a primary and the rest of them being a secondary.

in example,
Code:
int vlan 10
  ip addr 10.1.1.1 255.255.255.0
  ip addr 10.1.2.1 255.255.255.0 secondary
  ip addr 10.1.1.2 255.255.255.128 secondary
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