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9 votes
Accepted

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

Why does MPLS need an IGP (like OSPF) in order to work? In an MPLS network, OSPF is not used to route customer traffic. It is only used to provide routing for the internal provider network so that ...
Ron Trunk's user avatar
  • 67.7k
6 votes
Accepted

Does one logical router have only one route table?

Yes. One router have one forwarding table (FIB). It filled by routing protocols from their RIB. Often device can have different FIB's for different type of traffic (i.e. unicast and multicast). Each ...
Andrey Prokhorov's user avatar
6 votes

What are any disadvantages of redistributing eBGP routes into IGP

To answer your specific question: no, there's no "conceptual" or fundamental reason not to redistribute. There are a few practical considerations, but you seem to already be aware of most ...
Ron Trunk's user avatar
  • 67.7k
5 votes

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

So, why to use also MPLS if we already had OSPF? Downsides of IGP Metric based: There will be a segment underutilized as you can see from the link cost. Traffic for the different networks attached ...
DRP's user avatar
  • 1,491
5 votes

Hot Potato, algorithm of selecting route in router

Is my algorithm correct? Not exactly. Routing protocols do not route. A router can route without even using a routing protocol. Routing protocols simply exchange routes with other routers. The router ...
Ron Maupin's user avatar
  • 99.8k
5 votes
Accepted

EIGRP failover - how do i verify it happened?

There is a command made for such checking. Use: show ip eigrp events
Viktor Borisov's user avatar
4 votes

EIGRP failover - how do i verify it happened?

Yes, you can confirm that. Once hold-time expires, the former feasible successor route immediately becomes the successor route and is installed in routing table. I do not think we have a log message ...
Hung Tran's user avatar
  • 3,754
3 votes
Accepted

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

BGP generally assumes that AS is running an IGP, to interconnect its routers. When R_Q receives a route that goes through R_P, it will have to lookup a route to R_P route through IGP as a part of BGP ...
Effie's user avatar
  • 1,828
2 votes
Accepted

Do I understand IP Routing correctly?

Hosts contain their own routing tables, and will consult those to determine whether the packet can be delivered directly, or forwarded to a gateway (and if so, which one). Only then does your step 1 ...
Alnitak's user avatar
  • 246
2 votes
Accepted

EIGRP delay summarization?

What your drawing has is one, or both, of the routers overriding the interface delay. Under normal circumstances, the delay of a link is exactly the same on both ends. One of the routers may be doing ...
Ron Maupin's user avatar
  • 99.8k
2 votes

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

Since you'll be doing eBGP at both locations, any update received will be subject to BGP loop prevention, which is - any prefix received with the local ASN present within its' AS-Path attribute, will ...
Alex's user avatar
  • 21
2 votes
Accepted

What are LDP-MPLS advantages?

In todays routers routing lookup is done in hardware, usually in TCAM, which is as fast as ILM lookup. So no advantage in lookup speed. So why is it even needed? For tunneling. If you want to deploy a ...
manish ma's user avatar
  • 1,624
1 vote

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

From: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bgp/command/irg-cr-book/bgp-a1.html?bookSearch=true#wp4270480859 Command Default In releases prior to Cisco IOS Release 15.1(2)S, 15.2(...
manish ma's user avatar
  • 1,624
1 vote

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

BGP will not install a route to routing table unless its next-hop adress is reachable. This reachability can be achieved however you like. Maybe even using BGP itself to advertise this next-hop👀.......
manish ma's user avatar
  • 1,624
1 vote

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

Routing protocols have a priority value called Administrative Distance(AD). If two routing protocol processes with different AD values send the same route to RIB, the one with the lowest AD will be ...
manish ma's user avatar
  • 1,624
1 vote

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

MPLS is used to tunnel traffic over MPLS core routers to reach BGP NHs of BGP destination networks, since these MPLS core routers probably didn't learn (and probably shouldn't learn) the destination ...
manish ma's user avatar
  • 1,624
1 vote

Do I understand IP Routing correctly?

Routers don't "ask" each other about routes when deciding where to send a packet. The routes a router knows about are determined in advance, either statically or by routing protocols. To reduce the ...
Peter Green's user avatar
  • 13.3k
1 vote

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

Traffic in a network can be divided into 4 categories. Ingress: traffic arriving from outside the network, destined for hosts within the network. Egress: traffic originating inside the network ...
Peter Green's user avatar
  • 13.3k

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