What you need to watch out for as you build your GRE tunnel is how you learn the tunnel destination address
the DSG suggests the connected AD 0 network as the tunnel destination which is fine, but if you build the destination address as one which is further upstream im sure you'll get a recursive routing issue some example addressing below: 100.100.100.100/24 area 0 network tunnel0 ip's 192.168.1.1/30 area 0 tunnel source 10.0.0.1/24 area 1 tunnel destination 20.0.0.1/24 area 2 the definition of this problem is to get to network x which is learnt via the tunnel peering, then i need to know how to get to tunnels destination address which itself is learnt via the tunnel peering so the data-plane packet which is built would be GRE s:10.0.0.1 d:20.0.0.1 < 192.168.1.2 ipv4 header s:192.168.1.1 d:100.100.100.100 so our genuine tunneled traffic is sourced from the tunnel interface itself (icmp ping) with the destination as the 100.100.100.100 network ok cool..... but the destination address in the tunnel should be what we've declared in the interface tunnel statement i.e 20.0.0.1 but the problem comes when we try to build this tunnel destination address it actually becomes the tunnel's area 0 peering address i.e 192.168.1.2 this is where the recursive lookup happens to get to 20.0.0.1 we have to go though the tunnel and to get to the tunnel destination we have to get to 20.0.0.1 and vice versa, hence IOS protects against such recursions and will shutdown the tunnel interface. I think that's right you can overcome this by using a static route AD 1 to the tunnels destination address going via the physical interface hence beating AD 110 learnt via the logical tunnel interface but really just use the connected interface as in this lab by virtue of a VL being built between R8-R7 then R8 is an ABR & that is where we need to get too.. -- BR Tony > On 20 Feb 2014, at 15:44, Ryan Jensen <[email protected]> wrote: > > I had a question regarding step 13. > DSG suggests creating a GRE tunnel between R7 and R8 and putting that link > into area 0. Why do you put it in Area 0? Does that work because we already > have a virtual link from R7 to R5? Would it still be 'correct' if i made > the GRE tunnel between say R8 and R5 or R6? > _______________________________________________ > Free CCIE R&S, Collaboration, Data Center, Wireless & Security Videos :: > > iPexpert on YouTube: www.youtube.com/ipexpertinc _______________________________________________ Free CCIE R&S, Collaboration, Data Center, Wireless & Security Videos :: iPexpert on YouTube: www.youtube.com/ipexpertinc
