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26

Can anyone explain me what is the need of IBGP communication for the routes, when we have the IGP protocols (OSPF, RIP) for internal communication? Scalability1: Imagine that you're receiving 500,000 EBGP routes in more than one location2, and you need to influence the per route exit point in your AS. BGP can handle many more routes than IGP protocols. ...


10

iBGP requires a full mesh or use of mitigation like confederations or route reflectors, BGP doesn't converge with anything like the speed of OSPF, etc. Each OSPF router would have a full understanding of all the routes that are in the area in which it resides without needing a full mesh, and it converges very, very quickly. Using an IGP is recommended with ...


10

IGP usually is OSPF or ISIS which are link-state based, this gives us all the information of the network, everyone knows network from everyone's point-of-view, which allows for very interesting convergence options and traffic engineering options. BGP is essentially distance-vector, it knows very limited view on the network at whole. BGP handles very well ...


9

First off, I would dispute the assertion that some others have made that OSPF converges faster than BGP, but more on that later. To answer the OP question first. You want both. iBGP is designed to run between loopback interfaces on routers and it doesn't (at least without tweaking and turning some knobs) change any attributes (which includes next-hop) of ...


8

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 labels can be generated. LDP is used to advertise these labels to neighboring label-switched routers. So, why to use also MPLS if we already had OSPF? You'...


7

One reason I've seen quite often is clarity: all routes are carried within one routing protocol (BGP), IS-IS, OSPF or RIP is only used for adjacency. As a result there is no need to redistribute routes from one routing protocol to another.


6

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 routing protocol have own routing table (RIB). You can create isolated FIB by using VRF's (Cisco) or routing-instances (Juniper).


5

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 for E will always take the same path. The bigger the network the more the impact. Pattern unaware: Traffic patterns on the network are not taken into account ...


5

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 will determine which routes populate the routing table from various sources, including routing protocols, based on things like reliability of the prefix source,...


5

Do eBGP routers send their routing tables to all routers (both BGP and IGP) in one AS? No, that's the whole point of running a separate protocol. BGP speakers redistribute a very small number of routes into the IGP. If you only have one link outside your AS, then the BGP router just needs to redistribute a default route. If you have more than one exit ...


5

There is a command made for such checking. Use: show ip eigrp events


4

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 of when a feasible successor route becomes a successor route, given the fact that it happens right at the same time when the message of Neighbor 192.168.14.17 (...


4

There are multiple ways to do this. The other ASes could be sending a default route, or the router in AS100 could just have a default route configured. The other ASes could just advertise their own routes through BGP. The other ASes could advertise full BGP routes to AS100. BGP has many factors which could play into the decision of which way to switch ...


4

RIPv2 with the no auto-summary option will advertise the specific routes, not the aggregated prefix, unless you you use the ip summary-address rip interface command. The network statements in RIP are not specifically telling RIP what prefix(es) to advertise, they tell RIP which interfaces should participate in RIP, and RIP will get the specific prefix(es) ...


3

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 route calculation if R_Q cannot find a route to R_P it ignores the route at some time in BGP decision process, the IGP metric for the route is taken into ...


3

BGP protocol is the routing protocol of the INTERNET. IT´s the way that all the autonomus systems are interconnected. The BGP is conformed by 2 types of peers, internal and external peers(from the AS point of view). Then, you, like a network administrator, need to know the networks that you want to announce to the world(once that you have been approved by ...


3

iBGP isn't really used for internal routing, it is used by all your eBGP routers to share their routes. Ex: If you are peering with 3 other network, you want all your eBGP routers to know the routes received by the other ones so they can propagate that information to the peers if necessary/needed (opening thus the possibility of your peer using transit ...


3

While everything @RonMaupin says is true, in your particular case, with only five routers, there is not a lot to be gained by adding another routing protocol. Since you don't have a full mesh, you will have to configure your core routers as route reflectors. The only real downside is that BGP converges more slowly than OSPF, but there are ways to ...


2

I have had also similar situation. It depends on different factors. I assume that your topology won't scale that much, so I would suggest keep going with BGP as you mentioned good pros for that. Also, you can implement BFD to have faster convergence and dead peer detection. Regarding the connection type, VPN over Internet would by last option, because ...


2

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 start. Your final step is completely incorrect. At no point does a router "ask" its neighbours for a route to a specific destination. The routing protocols ...


2

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 that on purpose to influence routing. Changing the delay is a common way to influence routing. The other way would be to manually change the bandwidth, but that ...


2

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 be dropped. Hence, announcements from Site-A, will not reach Site-B. Which might not be a problem after all, if your ISP advertises a default-route only, to ...


2

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 full-mesh of tunnels dynamically between routers (usually PE routers) you can use LDP. This provides infrastructure for services like L3VPN, L2VPN etc.


1

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👀....but its probably a bad idea (since you don't want these addresses to be reachable from other ASes). Note that RR doesn't have to be in the path to reach the ...


1

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 selected and installed. In your case you have: OSPF (110) , EIGRP(90) and external (redistributed) EIGRP(170). So, the EIGRP routes learned directly from an ...


1

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 NLRIs via BGP. In case of L3VPN for example, without MPLS it would be necessary for all provider core routers to know all customer's routes via BGP, each in its ...


1

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 size of routing tables summarisation techniques are employed. Within your site you need routes for each of your subnets. Ideally your ISP only needs a route for ...


1

While I'm not a fan of IGP over WAN circuits (mostly due to the low circuit speeds which could cause convergence problems if there are many branch sites), I have seen this work well. There is no single answer of eBGP, iBGP, or IGP for a WAN since there are a lot of factors to consider. Traditionally, the WAN topology would be a hub-and-spoke with the ...


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