Questions tagged [ospf]

For questions about OSPF. Open Shortest Path First (OSPF) is a link-state routing protocol for Internet Protocol (IP) networks.

Filter by
Sorted by
Tagged with
26
votes
7answers
7k views

Does it make sense to deploy OSPF across Metro Ethernet?

When I need to connect a number of branch sites to one another for a customer, I typically recommend an MPLS VPN through a trusted carrier. The CE at each site speaks BGP with its upstream PE and each ...
22
votes
4answers
67k views

Why must all areas connect to an Area 0 backbone in OSPF?

This question is a literal repost of the same question asked on The Cisco Support Community. Answers are unique to Stack Exchange. Why is area 0 the backbone area in OSPF? Why must all other areas ...
22
votes
4answers
49k 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 ...
22
votes
3answers
61k views

Protocols: EIGRP vs OSPF [closed]

EIGRP and OSPF are both IGP protocols, the former is a mostly Cisco protocol and the latter is a well established open standard. What are the benefits of one over the other? Put another way, when ...
19
votes
2answers
2k views

How do you get an ASA to announce NAT'd 'outside' addresses in to an OSPF zone?

Device arrangement is as follows: BGP Peers + | | +------+-------+ | | | Juniper MX5 | | | +------+-------+ |.254 OSPF | 10.0.1.0/24 ...
16
votes
4answers
5k views

Why does this router fail to use multiple, equal-cost routes from OSPF?

A Brocade router running NetIron 5.2, and a Dynamips emulation running IOS 12.4 both fail to dependably use equal cost paths in what seems to be a very simple configuration. I say "dependably" because ...
15
votes
6answers
2k views

Securing OSPF with only passive interfaces

I know that to secure OSPF you should 1) use OSPF authentication, 2) use passive interface command on interfaces that do not have ospf neighbors. If I only use the passive interface command and not ...
13
votes
5answers
14k views

Why does OSPF need Type2 LSAs?

Learning more about OSPF for CCNP studies. I'm looking at how OSPF builds its links, and have just covered Type1 LSAs. Looking at Type1 LSAs, I'm wondering why these are even necessary? The book ...
12
votes
3answers
12k views

OSPF Stuck in Exstart Adjacency State

According to this article two routers will get stuck in the exstart adjacency state when their configured MTU sizes do not match. Does a VLAN tag affect this as well even if the routers involved are ...
11
votes
2answers
4k views

Why is RIP not scalable?

Most of the references say "RIP is not scalable" hence can be used only in smaller networks. But none say "WHY?" What is that in RIP that actually preventing it from scaling to larger networks? And ...
11
votes
3answers
4k views

OSPF over vPC on Nexus7k

I'm trying to help a friend with some Nexus issues. The topology is like this: Cat 3750 stack -> vPC -> 2x N7k -> LACP -> Fortigate firewall cluster The 3750 stack is running OSPF to both the ...
10
votes
2answers
5k views

Why does the MTU need to match on interior link state routing protocols like EIGRP and OSPF?

If one tries to configure the neighbor adjacencys without matching MTU, The routers fail to become neighbors. I assume this is to protect the routing protocol from it self but I don't understand ...
10
votes
3answers
1k views

OSPF link cost design

What kind of processes and/or tools do you use to design OSPF cost on links in your environments?
10
votes
3answers
4k views

3 subnets, 2 OSPF areas - Will This Work?

Will any issues occur if I have a topology involving 3 subnets and two OSPF areas where one subnet is in AREA 0 and the other two subnets are both in AREA 1? For example: [area 1, subnet 1]---[ABR #...
10
votes
3answers
21k views

Whats's the function of a loopback interface in routing protocols?

So I've got this task where I have to setup a virtual network with an OSPF routing protocol. I firstly ignored this loopback interface I had to configure on the routers since it didn't do any ...
9
votes
4answers
44k views

What is the advantage of an “area” in OSPF configuration?

As we know, during OSPF configuration we use the area. Each area has its different number, while there is only one area (area 0) which creates communications between all other attached areas. I am ...
9
votes
3answers
16k 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 ...
9
votes
3answers
3k views

Using latency to calculate OSPF metrics

Is it possible to configure OSPF to use latency in its link cost/metric calculations. The idea being to enable performance based routing whereby the fastest and least congested links in the network ...
9
votes
4answers
12k views

OSPF Election with a /30 link?

I have a few /30 subnets connecting OSPF routers over a broadcast capable link.. Should I also configure the interfaces involved in the link to ip ospf network point-to-point? Or does it matter? The ...
9
votes
1answer
2k views

Summarized OSPF routes advertised?

Preparing for CCNP, doing some lab work. ZEUS is summarizing two loopbacks with area 2 range 172.16.2.0 255.255.254.0, and the summary route is arriving on router 'WODAN' but the subordinate routes (...
9
votes
1answer
316 views

Remote Campus Routing Design

A third party provider supplies connectivity my remote satellite campus over metro ethernet. Due to red tape the provider is required to supply a routed point-to-point connection (R2 and R3) to the ...
9
votes
1answer
2k views

JUNIPER: Why is OSPF adjacency breaking when I enable FBF on an OSPF interface?

I've built a test lab where I am testing Filter Based Forwarding (FBF), aka Policy Based Routing. Question will follow below, but first, the details: Below is the topology diagram: OBJECTIVE: Any ...
8
votes
2answers
1k views

OSPF increase bandwidth with load-balancing

This is my current setup where i have 40Gbps links between all 4 switches running OSPF using L3 links between them but now i want to double my bandwidth between switches so i am planning to add (...
8
votes
1answer
684 views

Why have all my lab routers set their OSPF priority to 0?

I have 4 routers in my lab. FR1 is the frame relay switch (2621), R1(2621), R2(2651) & R3(2651) are all connected in a mesh using sub interfaces - R1 has pvc to R2&R3 and so on. Without OSPF I ...
8
votes
1answer
2k views

Wireshark Filter - OSPF Database Description Link State ID

Within Wireshark, how would one write a display filter for the IP address of the Link State ID within an OSPF Database Description packet? The Link State ID addresses are found within the LSA Header ...
8
votes
1answer
591 views

Struggling inbound and outbound traffic engineering to/from iBGP peers at different POPs

We are a managed service provider running a small sized network in a single datacentre in Sydney. We've recently deployed a new POP inter-state in Melbourne (both are on the east coast of Australia), ...
8
votes
3answers
2k views

OSPF Backbone Area and the WAN

I am working on a new network deployment, and have run into an interesting question... Should the OSPF area 0 be extended across a WAN's point to point links (thereby creating more border routers), ...
7
votes
4answers
19k views

What is Null 0 interface?

In which case is ip route 10.1.0.0 255.255.255.0 null0 used? Thanks in advance. This question is a repost of the same question in The Cisco Learning Network; however, the answers are unique to ...
7
votes
4answers
9k views

Distributing static routes across an OSPF area

If you have a router which does not support OSPF, but your routing topology makes use of OSPF as all other devices do support it, what is the best way to get this routers networks in to the OSPF area? ...
7
votes
3answers
3k views

OSPF and its use of Multicast

When it comes to OSPF and its use of multicast, am I correct in believing that IGMP forwarding and an IGMP querier is still required within the local segment? My understanding would be without this, ...
7
votes
4answers
8k views

How OSPF decides a network to be a stub network?

In RFC 2328 it mentions that link-state information of all Loopback interfaces and all interfaces with network mask as /32 (host ip addresses) are advertised as stub network type. Now what about the ...
7
votes
3answers
38k views

Why do we use OSPF Point-to-Point Networks for Loopbacks?

Why do we use the ip ospf network point-to-point command on loopback interfaces? interface Loopback0 ip address 2.2.2.2 255.255.255.0 ip ospf network point-to-point kindly explain that..
7
votes
1answer
645 views

Can we do redistribution of ipv4 routes onto v6 address families?

Iam just curious to know whether ipv4 routes can be redistributed to ipv6 address-families. Eg: I have a router for BGP configuration with ipv6 address-family and OSPF in ipv4 with other neighbor. Can ...
7
votes
3answers
8k views

Split OSPF Area 0 Behavior - What happens?

To make my question as simple as possible, I put together a quick scenario: Area 0 spans two data centers with multiple routers/networks in each. Area 0 has two ABR's connected to area 1 that connect ...
7
votes
2answers
646 views

OSPF on ASA 8.2 not advertising /32

We have set up OSPF between our 2 ASA 5540 running in Active/Passive and our Internet provider's Juniper routers. We would like to advertise routes based on the content of an ACL through a route-map : ...
6
votes
3answers
11k views

OSPF and routing table

I have several questions on OSPF. 1 OSPF is a link-state prototol, so routers inside an AS only broadcast their link states to all the other routers. I'm wondering if a router doesn't tell other ...
6
votes
3answers
11k views

What is the difference between broadcasting and flooding?

In Open shortest path first routing algorithm, the information about connected links is "flooded" throughout the network. How is flooding different from broadcasting?
6
votes
3answers
1k 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 ...
6
votes
1answer
3k views

Network not participating in OSPF. Does not appear in the routing table

I am running OSPF on 2 router in GNS simulation for practice. Adjacencies are ok. Router R2 has in the routing table all networks of R3 . But R3 fails to add R2 network in its routing table . The ...
6
votes
2answers
463 views

Metro Ethernet settings on Customer devices

I am about to connect three remote sites to the main office by means of an metro ethernet provided by a service provider. The sites are connected by means of l3 and running OSPF on the connecting ...
6
votes
4answers
11k views

When/Why to use OSPF?

This question has been hanging around in my head for a while; all the way from back in 2012, when we replaced our core network switch. This switch was actually a stacked pair of old 3Com 4900sx, and ...
6
votes
2answers
4k views

OSPF manual neighbor configuration requirement on NBMA network

Why are OSPF neighbors manually configured on NBMA networks even when you enabled it with the broadcast keyword in frame map statements? Example is NBMA point-to-multipoint access. Thanks.
6
votes
1answer
922 views

OSPF backbone area design

I have a question regarding a hierarchical design of a campus network. Take a look at this image: If I understand correctly the links between each Area Border Router and BBone router are point-to-...
6
votes
1answer
124 views

How do I setup cisco router not to use the default route to look for internal networks that are down?

On the core router I use OSPF with other routers for internal networks and a default route to the ISP's router for Internet access. All internal routers have the CORE router as the default gateway. ...
6
votes
1answer
2k views

How to find a duplicate router-id ospf in the network?

Hi I've got a problem in the network with a duplicate OSPF router-id. We tipically use the loopback ip address as the router-id, but I'm afraid that someone in the network don't care about that. I ...
6
votes
3answers
3k views

OSPF default route, 2 routers connecting to ISP

At work, we have a network with 2 routers connected to ISPs, and other routers in our internal network like this: ISP ISP |(BGP) |(BGP) R1 ...
6
votes
3answers
3k views

Quagga OSPF DR/BDR Mismatch: Losing Routes

I am experiencing a problem with lost routes in an OSPF over DMVPN environment. I am running ubuntu server 14.04 with Quagga 0.99.22.4, and OpenNHRP 0.14.1. While technically the DMVPN network is an ...
6
votes
1answer
222 views

Router Ethernet port ip no accessible from clients

I have this setup with a hybrid of equipment's from Cisco and Ubiquiti Edge routers and Vyos. My Cisco Nexus configured with HSRP with all the SVI's on 192.168.1.243 as the active on HSRP and SVI's ...
6
votes
1answer
5k views

Assistance with routing between layer 3 switches with ospf

I have two Cisco 3560's in a branch office. One acts as an access switch configured with two vlans: interface Vlan10 ip address 192.168.0.254 255.255.255.0 interface Vlan20 ip address 172.16.0.254 ...
6
votes
2answers
2k views

OSPF Route Tagging and BGP AS Prepend

Is it possible to perform the following configurations on Cisco routers, and are there any challenges with these types of configurations (mainly #3)? Match an OSPF route tag of 12000 (Definitely ...

1
2 3 4 5
8