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Questions tagged [igp]

For questions about IGPs (Interior Gateway Protocols), which are routing protocols used within an AS (Autonomous System).

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24 votes
7 answers
58k views

Why use iBGP inside an Autonomous System, if IGP protocols fulfill the need for internal communication

Can anyone explain why we need iBGP for the routes when we have the IGP protocols (OSPF, RIP) for internal communication within the AS? I have read a lot of articles and books, but I could not find ...
user2720323's user avatar
  • 1,611
10 votes
3 answers
27k views

OSPF or iBGP for interior routing protocol?

So the plan is, two core routers each with a eBGP session to one of two ISPs with full routes. Both routers publish their full tables to each other so they can control traffic flow more intelligently ...
OJS's user avatar
  • 343
9 votes
4 answers
2k views

BGP - how does IGP know the right route?

Let's consider a host A in an autonomous system AS100. Suppose it wants to communicate with host B in another AS, say, AS200. In AS100 there are several routers. Within one AS, the rotuing protocols ...
user4205580's user avatar
5 votes
3 answers
11k views

Why does MPLS need an IGP (like OSPF) in order to work?

I saw a network using MPLS, BGP and OSPF as main network protocols. I understand that BGP was used to exchange traffic with another AS, and OSPF was used as Internal Gateway Protocol. So, why to use ...
heavymeza's user avatar
4 votes
1 answer
243 views

Does one logical router have only one route table?

If a router running several IGP, such as two EIGRP processes, one OSPF: Will all the IGPs processes' acquired routes be stored in the router's one and only route table or more? I mean, two ...
lustre's user avatar
  • 155
4 votes
2 answers
337 views

Hot Potato, algorithm of selecting route in router

I want to understand a "hot potato" principle. Given a router with 5 interfaces. The first interface gets a packet and has to decide to which interface this packet should be forwarded. I think the ...
ruProgrammer's user avatar
3 votes
2 answers
726 views

EIGRP failover - how do i verify it happened?

I have 2 links to a destination and EIGRP was setup. The faster link is the successor and the slower link is the feasible successor. Switch1#show ip eigrp topology 192.168.1.0 EIGRP-IPv4 Topology ...
Noob's user avatar
  • 529
2 votes
2 answers
470 views

What are any disadvantages of redistributing eBGP routes into IGP

I wonder if there are any conceptual disadvantages of redistributing routes learned through eBGP peerings into an IGP, like OSPF. I have read of course about performance issues and the risk of ...
Patrick Aszody's user avatar
2 votes
2 answers
453 views

How do two clients of a route reflector learn about each other when no IGP/static-route is used?

I recently learnt that Route reflectors are an efficient alternative to full mesh IBGP peering in a large AS. Imagine a network like: D1 - AS1 <e> R_P <i> RR <i> R_Q <e> AS3 - ...
Jayanth's user avatar
  • 27
2 votes
1 answer
18k views

RIPv2 manual subnet mask configuration?

As I understand Cisco IOS takes subnet mask from interface to which is network connected and put it in RIPv2 updates. Could you advice please if it possible to somehow manualy set subnet mask of ...
DmitriiGangan's user avatar
2 votes
3 answers
264 views

Do I understand IP Routing correctly?

So I'm revising for a Networking exam and struggling to understand IP routing. If I explain how I understand it, could you tell me where I'm right and where I'm wrong? I'd really appreciate it. Here's ...
Jansky's user avatar
  • 123
2 votes
2 answers
906 views

Routing between branches

I have always used eBGP (with private AS numbers) to route between branches and headquarter sites. However, after reading the Cisco CCNP ROUTE Foundation Learning Guide, it states that best practice ...
Michael May's user avatar
  • 1,005
2 votes
1 answer
140 views

What are LDP-MPLS advantages?

An LDP-MPLS is deployed on a network and labels are used for packet forwarding. As you may know, LDP needs IGP and there is IGP too. Because there is no RSVP, there is no traffic engineering and there ...
A.A's user avatar
  • 551
2 votes
1 answer
867 views

Does the iBGP belong IGP?

We know the iBGP in the AS can transmit the BGP data, it running in the AS, is it belong IGP?
three-blocks's user avatar
1 vote
1 answer
511 views

One AS, Multiple Site with different physical location and ISP, different prefix

I am looking to implement few servers at different location with own ASN having prefix of PI resources of /22 going to divide into 2 x /23. I am unaware of what challenges I can face. As the 2 sites ...
Saurabh Sonar's user avatar
1 vote
1 answer
113 views

EIGRP delay summarization?

Could you please explain why when sending EIGR updates only delay of incomig interfaces are summarized and delay of outgoing interfaces is not considered. Please see picture below:
DmitriiGangan's user avatar
1 vote
1 answer
94 views

Does the Router running multi routing protocol progresses received the routes will store into the Forwarding table?

I have a question about the Router running multi routing protocol progresses. if the bellow snapshot R1 have EIGRP and OSPF progresses, if the EIGRP progress received the routes from R3, will it store ...
three-blocks's user avatar
0 votes
1 answer
235 views

In a PE-CE network, we would redistribute routes between BGP and IGP without `bgp redistribute-internal`. How does redistribution works?

In a PE-CE network deployment on Cisco IOS/XE devices like - +-------------+ ...
Deepak's user avatar
  • 707