Re: EIGRP Neighbours

You are exactly right, this is because the mask is not exchanged in the
hellos. OSPF hellos contain the mask, which is compared to the interface
mask.

On Mon, Jul 6, 2009 at 2:39 AM, Jonathan Monkey <
jonathan.ccie_at_googlemail.com> 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
> R1 <http://129.1.17.7/24%0AR1> IP -> 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> 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
> >
> >
> > 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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-- 
Bryan Bartik
CCIE #23707 (R&S), CCNP
Sr. Support Engineer - IPexpert, Inc.
URL: http://www.IPexpert.com
Blogs and organic groups at http://www.ccie.net