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Bronze

do we really need BGP ?

Hi everybody

Here is what my book says about the possible application of BGP

"  The big motivation to use bgp occurs when you want to influence which link is used for certain destinations in the internet"

To make its point, author presents the following case:

  

The Caveat is

Traffic destined at 199.199.199.0 from company must use link 2

My argument is we can achieve the desired goal without using BGP.

For example ;  (  option 1)

We statically create default routes on R1 and R2 pointing towards ISP and then redistribute them into Company's IGP

We will have ISP ( the company already owns 100.100.0.0/16 and this prefix length was not assigned by Company's isp) advertises this prefix via bgp on internet.  ISP can create static route to 100.100.0.0 on its R1 and R2 pointing towards company's edges routers( R1 and R2)

we can create static route  on R1 and R2 inside company as shown below

R1 ip route 199.199.199.0 0.0.0.0 s0/0 ( Link 2 )

R2 ip route 199.199.199.0 0.0.0.0  ss0/0  (link2)

Then we can redistribute this prefix on R2 into company IGP with a better metric.

We redistribute this prefix on R1 into company's igp with a higher metric than R1's.

The result  all the traffic destined to 199.199.199.0 will be directed towards R2 which in turn sends them via link 2 to 199.199.199.0

====================================================

Option 2:

We can achieve the same goal by using PBR on R2 and R1

We can  configure a policy   on all the interfaces that connect R1 to company's core network.  We define the policy  all the incoming traffic entering those interface and going to 199.199.199.0  will be forwarded to R1 as long as there is IP connectivity between R1 and R2's s0/0( because S0/0 on R2 connects to isp,  we can use  track  command which will track SLA icm-echo operation between R1 and R2,s s0/0).

under normal conditions,  all the traffic destined 1to 199.199.199.0 will be directed towards R2 which will forward them  via link 2 .

If link2 goes down, the trackobject will go down  on R1 which will stop all the traffic going to 199.199.199.0  from being forwarded to R2. All the traffic therefore will use link 1 via R1 to reach 199.199.199.0

===================================

My point is we can achieve the  same goals without using BGP .So I am at lost  so as to why the author of my book argues for using BGP in the above case.

Your input will be greatly appreciated.

thanks and happy holidays!

1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Bronze

do we really need BGP ?

Aren't you concerned on the return traffic?

Using BGP allows you to manage traffic engineering much better than static routing.

While your current requirements will work w/o BGP, as the company grows and more routes need to be advertised and it can become quite a task.

Also, the ISP must implement static routing pointing back to your routers and delays may occur depending on their change management windows.

With BGP routing filtering and metric manipulation, you can control ingress and egress routing w/o involving the ISP on those changes.

BTW, you can have another option:

HSRP on R1 and R2 with object tracking. R2 will have a higher priority and decrement in case of link failure.

Core devices will point to the VIP, no need for IGP

2 REPLIES
Hall of Fame Super Bronze

do we really need BGP ?

Aren't you concerned on the return traffic?

Using BGP allows you to manage traffic engineering much better than static routing.

While your current requirements will work w/o BGP, as the company grows and more routes need to be advertised and it can become quite a task.

Also, the ISP must implement static routing pointing back to your routers and delays may occur depending on their change management windows.

With BGP routing filtering and metric manipulation, you can control ingress and egress routing w/o involving the ISP on those changes.

BTW, you can have another option:

HSRP on R1 and R2 with object tracking. R2 will have a higher priority and decrement in case of link failure.

Core devices will point to the VIP, no need for IGP

Bronze

do we really need BGP ?

Thanks Edison.

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