(BGP) Consider the following network: AS 65432 AS 2 AS 1 AS 3 AS 6 AS1, AS2, and
ID: 3912215 • Letter: #
Question
(BGP) Consider the following network: AS 65432 AS 2 AS 1 AS 3 AS 6 AS1, AS2, and AS3 are ISPs, peering with each other at the links between routers J-K, N-A, and D-G . AS6 is a customer of AS1 and AS3. Two more customer networks are shown All routers are shown. All links between routers are shown. All networks are running OSPF as their IGP, and al link costs are equal All providers are running I-BGP The prefix for AS6 is 12.2.0.0/16. The prefix for AS65432 is 135.207.16.0/20. The prefix for the nameless customer containing router S and host d is 192.20.225.0/24 AS1, AS2, and AS3 number their routers out of 1.0.0.0/8, 2.0.0.0/8, and 3.0.0.0/8, respectively DO not make any unnecessary assumption. If you have to make any assumptions they have to be reasonable and state them very clearly Suppose that AS6 announces the lower half of its address space (12.2.0.0/17) from the X-E link, and the upper half from the Y-C link. Let a's IP address be 12.2.33.65, and.b's IP address be 12.2.192.66. What is the path from a to b? From a to c? From a to d? From c to a? From d to a?Explanation / Answer
a to b: a->z->x->y->b (as all the networks runnning OSPF)
a to c: a->z->x->y->c (Y will be the connecting BGP router for c, as its Y-C link who has announced uppper half)
a to d: a->z->x->h->f->j->k->l->s->d (following OSPF OSPF inside network and IBGP between the networks)
c to a: c->e->x->z->a (x-e link has announced lower half)
c to d: c->b->a->n->k->l->s->d or c->b->a->n->m->l->s->d (c will reach it's border router using OSPF which is A, in AS2 there are two parallel paths to reach border router L which will connect to unnamed network via K & M)
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