Re: EIGRP Neighbours

At that point, both sides view each other as being part of the same
subnet (each address is reachable). So it still works.

The mask isn't contained within the Hello messages.

If you kept your .248 mask, but moved one IP address to .9, then it
would be outside the view of one side's interpretation of the subnet.
Therefore you'd keep getting "neighbor not on common subnet" one
whichever side had that .248 mask!

HTH,

*Scott Morris*, CCIE/x4/ (R&S/ISP-Dial/Security/Service Provider) #4713,

JNCIE-M #153, JNCIS-ER, CISSP, et al.

JNCI-M, JNCI-ER

evil_at_ine.com

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Jonathan Monkey wrote:
> If the masks are different EIGRP will still build it's peers
> Here is a test I did
>
>
> R1(fa0/0) <-> SW1
> SW1 IP ->129.1.17.7/24 <http://129.1.17.7/24>
> R1 IP -> 129.1.17.1/24 <http://129.1.17.1/24> -> Neighbourship UP
>
> Change R1 Subnet mask to
> Rack1R1(config-if)#int fa0/0
> Rack1R1(config-if)#ip address 129.1.17.1 255.0.0.0
> Rack1R1(config-if)#
> 2d16h: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 200: Neighbor 129.1.17.7
> (FastEthernet0/0) is down: address changed
> 2d16h: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 200: Neighbor 129.1.17.7
> (FastEthernet0/0) is up: new adjacency
>
> Rack1R1(config-if)#ip address 129.1.17.1 255.255.0.0
> Rack1R1(config-if)#
> 2d16h: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 200: Neighbor 129.1.17.7
> (FastEthernet0/0) is down: address changed
> 2d16h: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 200: Neighbor 129.1.17.7
> (FastEthernet0/0) is up: new adjacency
>
> Rack1R1(config-if)#ip address 129.1.17.1 255.255.255.240
> Rack1R1(config-if)#
> 2d16h: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 200: Neighbor 129.1.17.7
> (FastEthernet0/0) is down: address changed
> 2d16h: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 200: Neighbor 129.1.17.7
> (FastEthernet0/0) is up: new adjacency
> Rack1R1(config-if)#
>
> Rack1R1(config-if)#ip address 129.1.17.1 255.255.255.248
> Rack1R1(config-if)#
> 2d16h: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 200: Neighbor 129.1.17.7
> (FastEthernet0/0) is down: address changed
> Rack1R1(config-if)#
>
> So it looks like if they are in the same primary subnet, the peers
> should form
> The only instance where the peer did not form was when the Subnet mask
> on R1 excluded the host IP on SW1 from the IP range covered by R1
>
>
>
>
>
> On Sun, Jul 5, 2009 at 11:03 PM, Scott Morris <smorris_at_ine.com
> <mailto:smorris_at_ine.com>> wrote:
>
> That depends on whether you enjoy the repetitive "Neighbor not on
> common
> subnet" errors you'll get. :)
>
> You must match.
>
>
>
>
> *Scott Morris*, CCIE/x4/ (R&S/ISP-Dial/Security/Service Provider)
> #4713,
>
> JNCIE-M #153, JNCIS-ER, CISSP, et al.
>
> JNCI-M, JNCI-ER
>
> evil_at_ine.com <mailto:evil_at_ine.com>
>
>
> Internetwork Expert, Inc.
>
> http://www.InternetworkExpert.com
>
> Toll Free: 877-224-8987
>
> Outside US: 775-826-4344
>
>
> Knowledge is power.
>
> Power corrupts.
>
> Study hard and be Eeeeviiiil......
>
>
>
>
>
> hopalong wrote:
> > Hi
> >
> > Can anyone tell when EIGRP attempts to form a relationship, do
> the two
> > routers have to be in the same subnet? or do they just have to
> be in the
> > same major network?
> >
> > I seem to have routers that suggest that the second option is
> correct?
> >
> > Many thanks
> >
> >
> > Blogs and organic groups at http://www.ccie.net
> >
> >
> _______________________________________________________________________
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>
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Received on Mon Jul 06 2009 - 09:10:30 ART