Questions tagged [ospf]

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

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1answer
175 views

Difference in convergence time IPv4 vs IPv6

Using protocols like RIP, OSPF and EIGRP, would IPv6 converge faster in smaller network like 4 routers? Would it differ in bigger networks?
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1answer
128 views

In OSPF, do virtual links have a cost when looking at the routing table?

I have multiple routers connected to frame relay switches. I am using serial links from the routers to connect to the relay switches. I'm also using an unnumbered loopback address on all of the serial ...
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3answers
4k views

OSPF without Area 0

Once an interviewer asked me, "Can we use OSPF without area 0?" I was not able to answer at that time. Later on, I searched, but I did not not find a satisfactory answer for this question. So, can ...
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1answer
649 views

Prioritize redistributed BGP routes over OSPF intra-area

I have a few routers, each controlling a /16, connected together with VPN tunnels. These routers are all in the same OSPF area. Now, I'm also doing BGP with some other routers that I don't control, ...
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2answers
3k views

Why would Type-5 AS External OSPF Route not install in routing table?

I am redistributing an eBGP route into OSPF, I see the route flooded in the database, but it is not installed in the routing table on the other routers. What would cause this route not to install in ...
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1answer
1k views

What are disadvantage of Stub Area in OSPF?

Stub areas have many advantages, but can someone tell me what are their disadvantages?
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1answer
445 views

Why do I lose my OSPF routes?

I created little network and set up OSPF protocol. When I took away one ethernet cable I was hoping to see change in routing table... But what happened was that the router only showed directly ...
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2answers
602 views

Can an external default route be injected into a NSSA totally stub area?

According to what I learned from Cisco documents, by default a normal NSSA area's ABR does not create a default route. Unless you use the command: Area 1 nssa default-information-originate on ASBRs ...
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1answer
96 views

Does SPF algorithm find all possible paths through the LSDB?

When I read Cisco CCNP official guide, I found an explanation on how to calculate the cost of intra-area routes: Find all networks inside the area, based on the stub interfaces listed in the Type 1 ...
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1answer
3k views

OSPF between Cisco & PFsense

Cisco OSPF has area 0 with 10.0.0.0/24. PFsense OSPF has area 0 with 10.0.0.0/24 and area 10 with 10.10.2.0/24 and area 20 with 192.168.122.0/24. The routers have full "FULL/DR" & "FULL/BDR" ...
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4answers
1k views

Choosing a routing protocol

I have always wondered what causes an network engineer to pick EIGRP or OSPF over the other. Obviously OSPF is opened standard so can be used in a multi-vendor environment. If all equipment was cisco, ...
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1answer
1k views

OSPF doesn't work when one interface is shutdown

my topology along with IP and config: What I do: A. Normal tracert. With everything on/no shutdown, I do tracert from PC0|192.168.1.2 to PC1|172.16.1.2: C:\>tracert 172.16.1.2 Tracing route to ...
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3answers
3k views

OSPF configuration in MESH topology

Hi, I wanted to configure Multi area OSPF between these routers. I created test simulation on packet tracer. Can any one help me how I can do that because I am bit confused about the configuration ...
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3answers
413 views

OSPF - Lower RID elected as DR?

Two routers, ethernet link, priority both set to default of 1, R1 sits exclusively in AREA 1 with RID: 192.168.23.3. R2 is the ABR leading to AREA 0, RID: 192.168.23.2. No other routers in AREA 1. ...
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3answers
2k views

Can OSPF v2 and v3 coexist in the same router?

Can we run OSPFv2 on few interfaces and OSPFv3 on few interfaces within the same system? Can we run both OSPF v2 and v3 as different processes?
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1answer
447 views

What are the number of adjacencies in 10 router in mesh topology and DR/BDR topology in OSPF? [closed]

FYI: this is not a homework question. I was reading an article (http://packetlife.net/blog/2008/jun/19/ospf-network-types/) in OSPF and couldn't understand this point. "a segment containing ten ...
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0answers
235 views

OSPF question from ISP perspective

Was hoping for some advice regarding an OSPF solution for a customer. Basically the customer has about 4 sites. These would all be linked together physically. I have attached a basic network ...
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3answers
127 views

OSPF behavior on serial link, why neighborship formed even if interfaces belog from different network?

If two router are connected through a serial link, they form neighborship even if they belong from different network. I configured 1st router with IP 10.1.1.1/8 and 2nd with 10.1.1.2/16 and they ...
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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?
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2answers
186 views

OSPF (Quagga) complex network setup query

I'm currently have a bit of an issue setting up a network infrastructure that I need help with. My network infrastructure is: ____ ...
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1answer
2k views

ACL permit and deny to default gateway OSPF routing

I have the topology below: On the network 10.11.9.0/24 (Area 3), I want to allow only traffic to the Internet. How would I go about this as I was thinking denying traffic to all my network and allow ...
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1answer
44 views

Why RIP doesn't use the router IDs?

I know that OSPF uses router IDs, for example in LSDB. But, why doesn't RIP use router IDs for anything?
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2answers
2k views

Is there a way to detect whether router is ASBR in OSPF?

Am using open source OSPF software from ospf.org and running ospf daemon in host PC. If router has interfaces in multiple area, then its an Area Border Router. Is there a way to detect the router is ...
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1answer
314 views

Micro-BFD LAG and OSPF

When configuring a Micro-BFD session on a LAG, is it preferred/recommended to still also tie BFD to the OSPF adjacency that is established over that interface? I would think not as the BFD session ...
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1answer
473 views

dual homing WAN circuits BGP

we have the following scenario: MPLS_WAN_provider1 connects to our edge router1 via eBGP MPLS_WAN_provider2 connects to our edge router2 via eBGP Both edge routers are to connect to our LAN. We need ...
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1answer
618 views

Load balance between two edge routers using OSPF

Consider a scenario where I have two border routers one peering with ISP A and the other peering with ISP B. Let say I receive full tables from both ISP A&B. Internally we run OSPF and my ...
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2answers
362 views

IGP between 2 routers with an uncooperative router in the middle

I've got two routers, A and B. A gets some routes over BGP over a VPN connection, and has a leg on 10.0.0.0/24. It also can access the whole 10.0.0.0/16 via its default gateway. B is on 192.168.0.0/...
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2answers
1k views

How does OSPF understand its directly connected networks if you're configuring interfaces?

This is a question I've seen mixed answers for online, so I'll try to clearly explain what I'm having trouble understanding. With RIP, you have your router and you explicitly tell it your directly ...
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1answer
131 views

L3 Etherchannel cost calculation

Q1: I have read that in layer 2, if any of the links of a portchannel goes down,the cost of the portchannel is recalculated. Does that apply to L3 portchannel also? If so, assume I am running OSPF in ...
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3answers
153 views

OSPF Border Router Discovery

Hi how the routers in ospf network will discover the borders routers when i try to see the border routers with the show ip ospf border command i get : in Area 0 - R2 discover : all border ...
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1answer
213 views

What is the mathematical relation between MTU size and the number of LSA supported in OSPF?

Improved my calculation - based on the comments. However,I don't get the correct results yet. I am trying to find out the maximum number of stub LSA routes I can pass from one device to another ...
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3answers
2k views

OSPF question over dot1q trunk

above i have two L3 switches. ESW1 has vlan 10 and 20 ESW2 has vlan 10 and 30 (the same ten) when i configure OSPF on both ESW1 and ESW2 it doesn't neighbor. I want OSPF to advertise vlan 20 to ESW2 ...
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2answers
1k views

DMVPN + OSPF prevent traffic to flow through spoke

I have topology with two hubs and about 10 spokes running DMVPN(2 clouds) and OSPF over it. Like this: If 1gb/s link between main offices fail, traffic will flow through one of spokes, that mostly ...
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2answers
682 views

OSPF Point-To-Point Question

I've consulted the spec https://www.ietf.org/rfc/rfc2328.txt and have googled to the end of the internet but I'm confused on OSPF Point-To-Point. If I have the following: Link State ID: 4.4.4.4 ...
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1answer
1k views

OSPF setup between EX2200 and EX4200

Brief description: I have two juniper switches, an EX2200 and an EX4200. They are connected physically and OSPF is in the Full state, so they each see their neighbor, but they are not seeing the ...
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1answer
329 views

OSPF Routes not exporting

I have two routers (layer 3 switches to be honest: ex4200 and ex2200). I have zeroized both of them before starting this config. I have set up ge-0/0/12 on one as unit 0 family inet address 10.0.0.1/...
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4answers
2k views

What is the purpose of ospf?

I know what ospf is, but what purpose does it have in th efollowing scenario: an autonomous system has a single router which connects (through access switches) to hosts. The router also connects to ...
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2answers
90 views

In what case should the core router having iBPG configured or having routes redistributed via OSPF to it?

I have the following topology. The notebook computer has to access the internet. In what case should R3 (as the core router & default gateway for the internal network) having iBPG configured or ...
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2answers
286 views

Does the Shortest Path First algorithm (SPF) Algorithm for OSPF and IS-IS generate all shortest paths between nodes, or just one?

To be more specific. If there are two equal cost paths between two nodes, does the SPF Algorithm give the next hop value for both paths?
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2answers
868 views

MPLS VPN network using BGP, RIP and OSPF

I'm working on configuring a MPLS VPN network. Here is what I'm working with: From CE1 I would like to be able to ping the loopback address of CE2 and vice versa, which is not yet possible and I do ...
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1answer
4k views

Change OSPF Router ID without reload

We have setup OSPF on router and initial it pick ip address 70.xx.xx.33 but later we remove those IPs and reconfigure for new subnet but still OSPF showing older router ID sometime it's confusing ...
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1answer
322 views

OSPF Point to Point network ABR advertisements

Suppose ABR1 is an ABR which connects Area 1 to Area 0. Area 1 consists of routers connected via point to point links only (advertised by LSA 1). Is this correct that ABR1 will report all of these ...
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2answers
68 views

OSPF and addressing problem

I'm currently practicing setting up an MPLS VPN using GNS3. Here is the topology i have: I need to, on all P and PE routers enable OSPF routing protocol advertising all inside networks . From PE1 ...
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2answers
60 views

Dr election in partial lan connectivity

Suppose we have three routers R1 R2 and R3 with full mesh connectivity in OSPF broadcast network (LAN). R1 becomes DR. R2 BDR and R3 is forming adjacency with both of them. Now let router r4 be ...
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1answer
691 views

Managed MPLS CE router with BGP and OSPF

We have a scenario where a customer is having a managed L3VPN installed and would like to run OSPF internally. The issue is that the provider will not allow us to provide and manage the CE device and ...
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1answer
69 views

OSPF broadcast link - forming adjacenices between non-DR hosts

In an OSPF broadcast configuration, can some host (H1) form an adjacency with another host(H2) that is not DR. For example H1 does not see for some reason the DR advertised by the H2. Does standard ...
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1answer
148 views

OSPF DR/BDR question

I have an issue about OSPF. When I try to use "Show ip ospf neighbor" I can not find which router is the DR router or BDR router it always show "Full/-" Here is my set up Can someone help me, Thank ...
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2answers
91 views

OSPF Areas (OSPFv3 and OSPF)

If I have 4 routers, R1, R2, R3, and R4, and put all of the subnets from R1 and R2 in area 0, and put all of the subnets from R3 and R4 (including the routers) into OSPF area 1, would the ospf areas ...
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2answers
157 views

OSPF RFC2328: Why is a router connected to a transit network connected with two edges?

A transit network is represented by a graph vertex having both incoming and outgoing edges I can't say that this representation makes sense for me. Can anybody explain why the OSPF algorithm needs ...
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2answers
627 views

Trouble inserting static route into OSPF ASBR

Networking community, I was hoping someone might be able to provide me with some assistance in configuring one of my routers. Diagram below: Current configuration: The PfSense firewall is ...

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