Networking Administration


Networking Administration


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تمرین BGP

سلام به شما دوستان عزیز...
امروز یک سناریو آماده کردم که تقریبا تمام مباحث قبلی که توی وبلاگم گذاشته بودم رو در گیر میکنه...
متن سناریو به شرح زیر میباشد...
تمرین BGP

R1 has an EBGP peer to R5 and an IBGP peer to R2.
R2 has an EBGP peer to R4 and IBGP peer to R1.

Ensure that the 15 loopbacks on R1 (– are advertised to R5 and that R5 modifies all even networks with a local weight to 1000 and metric (MED) to 100. For all odd networks, set the weight to 2000 and the metric (MED) to 200.

Ensure that R1 advertises a default route to R5 and that R2 advertises a default route to R4. Use a prefix list to accomplish this task.

Ensure that R4 does not accept any networks in the range but does accept a default route only. All other networks must be denied on R4.

Ensure that R3 can reach all BGP-advertised networks using OSPF as the only routing protocol. (That is, redistribution is required on R1/R2).

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BGP Dual-Homing

In this scenario, you build upon the IBGP network  and configure EBGP on R1 and R2 and simulate a dual-homing ISP connection. Because most CCNP candidates do not have two ISP connections to configure in a lab environment, you configure two routers and inject default routes along with a large IP routing table to simulate an ISP router.

Configure the routers ISP1 and ISP2 for EBGP and advertise a default route to the internal BGP network along with some routes that simulate an Internet environment.configures ISP1(R6) for EBGP and allows a default route to be advertised to the EBGP peer to R1.

full pic duall-homin

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BGP Route-Reflector 1

سناریویی آماده کردم در مورد BGP Route Reflector .

Consider a network consisting of 100 routers. Having this many routers leads to alarge number of TCP BGP peers. In fact, you can easily calculate the number of peers by using the formula n(n-1)/2, where n is the number of BGP routers.

To avoid routing loops, BGP only propagates updates learned from IBGP connections to other IBGP sessions that are fully meshed. Fully meshed networks contain a BGP peer to every BGP speaker in the network. For a 100-router network, there are 100(100-1)/2 = 100(99)/2 = 4950 TCP peers.
IBGP works well in small networks, and as the network grows even to just 100 routers, the scalability and administration of BGP becomes a task you must carefully consider.
BGP deals with large BGP networks using two methods:
· Route reflectors
· Confederations (advanced form of route reflectors; confederations are beyond the scope of this chapter.)

شرح ، توضیحات و پیکربندی به شرح زیر میباشد.


the Routers R1–R5 are part of a large company and route reflectors are configured on R1 and R2 for redundancy purposes.Enable OSPF on the IGP routers by enabling all interfaces in area 0, so you can take advantage of loopbacks for the source and destination address for all IBGP peer sessions.

onfigure IBGP on R1 and use the loopback addresses as the next hop addresses because as long as you have IP connectivity, BGP should remain active. In
fact, good IBGP design always uses loopbacks so that one routing failure does not result in loss (TCP fails) of IBGP connectivity.

lo 0 for all routers : 131.108.254.x (x is number of each routers)

ospf configs on all router : R1-R5:

R1(config)#router ospf 1
R1(config-router)# network area 0

The reason that OSPF is chosen for the preferred path is that OSPF has a lower nadministrative distance of 110, compared to 200 for IBGP.

if EBGP is configured between two routers and OSPF is the interior routing protocol, EBGP administrative distance is 20, far lower than OSPF (AD is 110). By default, a lower AD is always preferred; therefore, the next hop address is the EBGP
314 connection.

To change this default behavior without the changing AD values, use the network <network subnet-mask> backdoor command. Specifying the network allows the router to choose OSPF as the preferred path rather than the EBGP discovered path.
Changing the administrative distance is not always the most desirable method because all routers typically need modification, as in this scenario.