usage of iBGP Peering

[harsha senaratna]

hi all ,

I did some labs in iBGP peering.  because using eBGP we can establish the peer relationship and through redistributing to IGP , propagate external networks to  the LAN. I want to know that exact purpose of this technology ?

If you can , It would be beneficial for me to elaborate them using real world example ?

Thanks

[Akash Agrawal · Accepted solution]

Hi,

There are many benefits of iBGP over IGP. Difficult to cover all but will try to list few

1. Scalability : If you are receiving full routing table from upstream which would be close to 500K. IGP can handle maximum 20-30K. Even if it handles 50K it is too less than full routing table.

2. Route stability: Since it is full global routing table, few routes flap is expected and if all routes would be in IGP it will make IGP core unstable and that cause high CPU also.

3. Enforce boundaries of trust / control: BGP has many more knobs than IGPs for controlling what you advertise and receive.

4. Custom routing policies: Implementing custom routing policies is possible in BGP with help of community,route-map, different attributes like Local-preference,AS-PATH.MED. In case of IGP we have only metric to choose best path.

5. If there is any low end router and you dont want to load that router with full routing table you can just pass a default route to that router via iBGP or IGP. But in case of IGP each router will have full routing table unless until you define that as stub router then it wont have even network infrastructure ips and TE will not be possible.

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Regards,

Akash