12
votes
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What is the difference between broadcasting and flooding?
Broadcasting is a term that is used on a broadcast domain, which is bounded by layer-3 (routers). Broadcasts are sent to a special broadcast address, both for layer-2 and layer-3. A broadcast cannot ...
- 98.8k
10
votes
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OSPF without Area 0
There is only one way to use OSPF without an Area 0, and that is to use OSPF with a single area. If you only have one OSPF area, you can number it any way you like, but if you have even two areas, you ...
- 98.8k
9
votes
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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 ...
- 67.1k
9
votes
OSPF and its use of Multicast
The benefit of multicast is that hosts not subscribing to the multicast group ignore frames they receive that are sent to the multicast group. With broadcast, they cannot ignore the frames.
The OSPF ...
- 98.8k
8
votes
What is the difference between broadcasting and flooding?
I will explain here in the context of switches (layer 2).
Flooding
When a switch receives a unicast frame (a frame with a specific MAC address intended for a particular device), it looks for the frame'...
- 181
8
votes
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OSPF Configuration: Router ID won't change to loopback address
Simply clearing the process may not be enough to re-start the RID selection process. That said, as Ron points out in the comments, it is by far best practice to manually specify the router ID in OSPF ...
- 6,104
8
votes
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Configuring OSPF on two directly connected routers which are in different areas
In order to connect two areas, one router has to serve as an area border router (ABR). That router has interfaces in both areas. In other words, the boundary between two areas is a router, not the ...
- 67.1k
8
votes
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OSPF increase bandwidth with load-balancing
As these are Point-to-Point links, I would consider using the outage to configure each /30 interface with ip ospf network point-to-point. (New and existing links). This reduces the hello and dead ...
- 1,241
8
votes
OSPF increase bandwidth with load-balancing
There's two ways to do that.
your proposed way, by adding a second link with its own /30 or /31,
making sure that OSPF installs multiple equal cost routes in the
routing table, and let CEF's ECMP (...
- 8,826
7
votes
Accepted
DR selection on OSPF
Let me clarify a misunderstanding: The DR is responsible for updating the LSDBs of the other routers on the network segment. It does not receive all the network traffic.
All the non-DR routers ...
- 67.1k
7
votes
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Routing loopback using OSPF
Loopback interfaces are considered as host routes, so they are always advertised with a /32 mask.
If you want to advertise the whole subnet, you have to change the network type to point to point like ...
- 67.1k
7
votes
Accepted
When would we use more than 1 dynamic routing protocol?
The administrative distance isn't about "trustworthiness", it's about preference - a combination of cost, delay, bandwidth, resilience, loss rate.
External routing and internal routing ...
- 82.7k
7
votes
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Layer choice for OSPF
OSPF is an application that exchanges layer-3 routing information with its OSPF neighbors. To do that, it has its own transport protocol (protocol 89) that uses IP to communicate with its neighbors.
...
- 98.8k
6
votes
Accepted
Whats's the function of a loopback interface in routing protocols?
The loopback interface is useful because it is an interface with an IP address which never goes down. OSPF, without a specifically defined Router ID, will pick a Router ID on its own. It chooses the ...
- 98.8k
6
votes
Accepted
I can't ping the other router using OSPF protocol, Why?
(I imagine your setup to be something like this)
Your OSPF adjacency is not coming up because the IP addresses on the facing interfaces between R1 and R2 are not in the same subnet.
As soon as you ...
- 311
6
votes
Accepted
When/Why to use OSPF?
Routing protocols, such as OSPF, are to share routes between routers. If your routing is done on a single router, or a pair of routers connected to the same networks (your layer-3 switches), it doesn'...
- 98.8k
6
votes
Accepted
What happens when a router receives an LSA with the same sequence nr?
Found the answer to my own question. When a router encounters two instances of an LSA, it must determine which is more recent. An LSA is identified by its LS type, ID, and LSA router. For two ...
- 181
6
votes
Accepted
OSPF configuration in MESH topology
The area design you have specified will not work. The interface and its adjacent interface need to be in the same area. You can't have one interface in area0 and the adjacent router interface in area1....
- 2,016
6
votes
Accepted
Why would Type-5 AS External OSPF Route not install in routing table?
capability vrf-lite is missing under router ospf
This article has a good explanation. Essentially, the command tells OSPF to ignore the DN bit and use the LSA in the SPF calculations.
https://...
- 76
6
votes
Accepted
Why does OSPF use flooding instead of broadcasting?
You are confusing the layer-2 flooding with OSPF flooding. The routers in an OSPF area may not all be directly connected, but every router in the area needs to have a full understanding of all the ...
- 98.8k
6
votes
Accepted
Struggling inbound and outbound traffic engineering to/from iBGP peers at different POPs
Both routes were External type 2, advertised the route as an OSPF E1, E1 is always preferred over E2 and this solved the issue.
- 1,491
6
votes
Accepted
Why OSPF E1 and E2 exist?
RFC 2328, OSPF Version 2 defines the Type 1 and Type 2 external metrics. Type 1 metrics are used if the primary cost is internal to your AS, but Type 2 metrics are used if the primary cost is external ...
- 98.8k
6
votes
Accepted
Question about OSPF and Database Descriptions
Isn't everything in the DBD which got send to him?
No, the DBD's only contain a summary of the LSA. To get all the LSA information, the router requests the full LSA from the neighbor.
It may seem ...
- 67.1k
6
votes
Accepted
What's the definition of Router Link and Net Link?
Router Link States are type 1 LSAs. It lists all the routers in the area and the number of interfaces. 2.2.2.2 has 3 interfaces.
Net Link States are the multi-access networks (Type 2 LSAs). The ADV ...
- 67.1k
6
votes
Which device initiates the data exchange in OSPF (is it the master device or slave)?
From "OSPF version 2" RFC 2328
During the Hello phase, every router sends packets:
Hello packets are sent periodically out all router interfaces. (section 7.1)
During database ...
- 16.2k
6
votes
Accepted
Why can the BGP protocol be implemented across routers, but the OSPF protocol can only be implemented direct connected routers?
OSPF was designed as an internal gateway protocol, to chose the best path in a network under your control. It would not make sense to connect non-adjacent routers, so that feature is not part of the ...
- 67.1k
6
votes
Passive interface default - issue
A passive interface in OSPF does not send hello packets, so it will never form a neighbor relationship nor exchange routes with another OSPF router.
By setting the passive interface default command, ...
- 67.1k
6
votes
Accepted
What Is The Difference Between Using Wildcard Mask In EIGRP And In OSPF?
I'll assume you are referring to the wildcard mask being used with the network ... statements in EIGRP and OSPF configurations.
As in (pseudo config code)
router ospf 100
router-id <...
- 8,826
6
votes
Accepted
What Happens If A Router Added To The Wrong Area Instead Of The Area 0?
1- Isn't OSPF a loop-free protocol? Shouldn't it avoid loops automatically?
OSPF is loop-free precisely because all inter-area traffic must go through area 0
2- What happens if we add new router R8 ...
- 67.1k
6
votes
OSPF ECMP on /32 - consequences on EVPN-BGP
OSPF does not do the (ECMP based) forwarding. OSPF just provides info that might make it into the routing table and further into to the actual forwarding table. And yes, there can be ECMP for /32 ...
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