February 03, 2006

debug ip ospf adj (Dailing Problem)

Yeah, here comes to the most common problem when deploying OSPF on a WAN network which using dialing technique.

-- Why doesn't OSPF form adjacency on a PRI, BRI, or dialer interface; and stuck on "EXSTART" state?

Designing OSPF to run on a temporary line will be an utterly catastrophic challenge to network engineers. And totally is a silly choice. I am fed up with solving my customers' network problems which due to the loathsome designing. Besides this P2P network type may lead to OSPF neighborship failure, ip ospf demand-circuit absolute a self-deceiving solution. It solve one problem by creating another, which drop OSPF network into terrible flapping. I like the words from Sam Halabi most: We deploy routing protocols because the network needs one, but not to show off our skill. The best routing protocol to be chosen is the routing protocol that fits the network infrastructure. We use a dialing layer-2 infrastructure ten to one goes to we are using it as a backup line. That's why I always recommend my customers using a static route on the dialing router instead of a dynamic routing protocol.

Let's look at the devil closely. And because we're talking debug ip ospf adj today, we may just observe the half face of it, the other half which come from ip ospf demand-circuit will be talked later next time.

The OSPF network-type on Primary Rate Interface (PRI), Basic Rate Interface (BRI), and dialer interfaces is point-to-point, which means that an interface can't form adjacency with more than one neighbor. A common problem when a PRI, BRI, or dialer interfaces try to form an OSPF adjacency is the neighbor gets stuck in the exstart/exchange process.

Let's look at an example:

Using the show ip ospf neighbor command, we can see the neighbor state is stuck in "EXSTART".
RTR-A#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface 1 EXSTART/ - 00:00:37 Serial6/0:23 1 EXSTART/ - 00:00:39 Serial6/0:23

RTR-B#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface 1 EXSTART/ - 00:00:36 BRI0

RTR-C#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface 1 EXSTART/ - 00:00:35 BRI0
We can debug this situation using the debug ip ospf adj command. Let's look at some sample output taken while running this command on RTR-B in the figure above:
1: Send DBD to on BRI0 seq 0xB41 opt 0x42 flag 0x7 len 32
2: Rcv DBD from on BRI0 seq 0x1D06 opt 0x42 flag 0x7 len 32 mtu 1500 state EXSTART
3: First DBD and we are not SLAVE
4: Rcv DBD from on BRI0 seq 0xB41 opt 0x42 flag 0x2 len 92 mtu 1500 state EXSTART
5: NBR Negotiation Done. We are the MASTER
6: Send DBD to on BRI0 seq 0xB42 opt 0x42 flag 0x3 len 92
7: Database request to
8: sent LS REQ packet to, length 12
9: Rcv DBD from on BRI0 seq 0x250 opt 0x42 flag 0x7 len 32 mtu 1500 state EXCHANGE
10: EXCHANGE - inconsistent in MASTER/SLAVE
11: Bad seq received from on BRI0
12: Send DBD to on BRI0 seq 0x2441 opt 0x42 flag 0x7 len 32
13: Rcv DBD from on BRI0 seq 0x152C opt 0x42 flag 0x2 len 92 mtu 1500 state EXSTART
14: Unrecognized dbd for EXSTART
15: Rcv DBD from on BRI0 seq 0xB42 opt 0x42 flag 0x0 len 32 mtu 1500 state EXSTART
16: Unrecognized dbd for EXSTART
Lines 1 - 3: RTR-B sends the first DBD to (RTR-A) with seq 0xB41 and receives the first DBD from (RTR-A) with seq# 0x1D06. Neighbor negotiation is still not complete.

Lines 4 - 6: RTR-B receives a reply from (RTR-A) indicating that RTR-A received RTR-B's first DBD. Since RTR-B has the higher router ID, RTR-A elects itself slave. After receiving the acknowledgement from RTR-A, RTR-B declares itself master and sends the first DBD with data in it. Note the sequence number, which is 0xB42. Since RTR-B is the master, only it can increment the sequence number.

Line 7: RTR-B requests data from RTR-A since RTR-A indicated it has more data to send (flag set to 0x2 in last DBD received from RTR-A).

Line 8: RTR-B sends a link-state request packet to (RTR-A). This is an OSPF packet type 3. This packet is usually sent to the neighbor's IP address. In this case, the neighbor's IP address is its router ID.

Lines 9 - 11: RTR-B receives a reply from slave (RTR-A) with a completely different sequence number and a flag of 0x7, which is the init flag. This DBD was intended for another router (most likely RTR-C), but RTR-B incorrectly received it. RTR-B declares there is a discrepancy because a flag of 0x7 means the slave has changed its status to master by setting the MS (Master/Slave) bit during the adjacency exchange. RTR-B also complains about the sequence number because it's out of order. The slave should always follow the master's sequence number.

Line 12: RTR-B re-initializes the adjacency by sending the first DBD to to re-elect master and slave.

Lines 13 - 14: RTR-B receives a DBD from (RTR-A), indicating that it's a slave, without recognizing RTR-B's sequence number. RTR-B declares that it doesn't recognize this DBD since the master and slave negotiation is not complete yet. This DBD packet was intended for another router.

Line 15: RTR-B receives a reply from (RTR-A) for the old DBD, but it's too late because RTR-B has already re-initialized the adjacency process.

Line 16: RTR-B fails to recognize this DBD because it is for an "old" adjacency, which RTR-B has already torn down.

This process will repeat endlessly.

The solution? The best solution should always be trying to change OSPF into static route.

OSPF sends a multicast packet for a point-to-point network-type even after the interface achieves the 2-way state. Since RTR-A is trying to form adjacencies with both RTR-B and RTR-C, RTR-B receives DBD packets meant for RTR-C and RTR-C receives DBD packets meant for RTR-B.

To solve this problem, change the network type on all routers to point-to-multipoint. This changes the behavior of OSPF to send unicast packets after the 2-way state. Now RTR-B receives only packets destined for itself and RTR-C receives packets destined for itself. Changing the network-type in this way ensures that the OSPF router will form adjacency on a PRI, BRI, or dialer interface.

To change the network-type, enter the following configuration commands. We'll change RTR-B as an example.
RTR-B#conf term
RTR-B(config)#int bri 0
RTR-B(config-if)#ip ospf network point-to-multipoint
Now if we look at the show commands for RTR-B, we can verify that the network-type is point-to-multipoint and the state is full.
RTR-B#show ip ospf interface bri0
BRI0 is up, line protocol is up (spoofing)
Internet Address, Area 2
Process ID 1, Router ID, Network Type POINT_TO_MULTIPOINT, Cost: 1562
Transmit Delay is 1 sec, State POINT_TO_MULTIPOINT,
Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5
Hello due in 00:00:16
Index 1/1, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 1
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor
Suppress hello for 0 neighbor(s)

RTR-B#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface 1 FULL/ - 00:01:36 BRI0
Related Links:


At 3/04/2007 07:55:00 PM, Anonymous Anonymous said...

best regards, nice info » »

At 3/28/2007 02:44:00 PM, Anonymous Trish said...

Thanks, very useful info!

At 12/02/2012 07:02:00 AM, Anonymous Anonymous said...

pozyczki online bez bik
pożyczki pozabankowe
pożyczki pozabankowe millenium
pożyczki bez bik
pożyczka bez bik
pożyczki pozabankowe 07

At 2/24/2013 10:08:00 AM, Anonymous Anonymous said...

[url=http://aaawatches24.co.uk/]fake watches[/url]

watch replica uk reviews
who sells the best replica watches
jimmy choo outlet
replica watches 4 uk review
replica watches review


At 3/28/2016 08:31:00 AM, Blogger oakleyses said...

burberry handbags, ugg boots, nike outlet, tiffany and co, christian louboutin, oakley sunglasses, ray ban sunglasses, replica watches, uggs outlet, uggs on sale, cheap oakley sunglasses, michael kors outlet, kate spade outlet, prada handbags, louis vuitton outlet, polo outlet, jordan shoes, tory burch outlet, oakley sunglasses wholesale, gucci handbags, replica watches, louis vuitton outlet, nike air max, louis vuitton, michael kors outlet online, christian louboutin shoes, prada outlet, chanel handbags, michael kors outlet, oakley sunglasses, ugg boots, oakley sunglasses, tiffany jewelry, uggs outlet, ray ban sunglasses, nike free, michael kors outlet online, nike air max, christian louboutin outlet, louis vuitton, longchamp outlet, christian louboutin uk, michael kors outlet online, ray ban sunglasses, polo ralph lauren outlet online, louis vuitton outlet, michael kors outlet online, longchamp outlet

At 3/28/2016 08:33:00 AM, Blogger oakleyses said...

mulberry uk, nike tn, abercrombie and fitch uk, nike air max, nike free run, lululemon canada, true religion outlet, oakley pas cher, longchamp pas cher, nike free uk, sac hermes, nike blazer pas cher, hollister uk, true religion jeans, new balance, air max, coach outlet store online, north face uk, coach outlet, north face, michael kors pas cher, true religion outlet, nike roshe run uk, nike air max uk, polo lacoste, michael kors, hollister pas cher, vans pas cher, nike air max uk, polo ralph lauren, jordan pas cher, timberland pas cher, nike air force, nike roshe, burberry pas cher, converse pas cher, michael kors outlet, sac vanessa bruno, ray ban pas cher, ralph lauren uk, kate spade, replica handbags, ray ban uk, michael kors, louboutin pas cher, true religion outlet, coach purses, guess pas cher, hogan outlet, sac longchamp pas cher

At 3/28/2016 08:35:00 AM, Blogger oakleyses said...

mont blanc pens, reebok outlet, mcm handbags, bottega veneta, abercrombie and fitch, hollister, nike roshe run, nike trainers uk, longchamp uk, celine handbags, insanity workout, iphone 6s plus cases, instyler, iphone cases, s6 case, mac cosmetics, herve leger, soccer jerseys, wedding dresses, north face outlet, new balance shoes, ferragamo shoes, iphone 5s cases, lululemon, ralph lauren, timberland boots, nike huaraches, soccer shoes, chi flat iron, asics running shoes, iphone 6s cases, jimmy choo outlet, valentino shoes, hollister clothing, iphone 6 cases, ipad cases, babyliss, vans outlet, nfl jerseys, north face outlet, giuseppe zanotti outlet, beats by dre, p90x workout, louboutin, oakley, ghd hair, baseball bats, hermes belt, iphone 6 plus cases, nike air max

At 3/28/2016 08:40:00 AM, Blogger oakleyses said...

hollister, coach outlet, barbour, canada goose outlet, ugg uk, wedding dresses, canada goose outlet, canada goose uk, toms shoes, doudoune moncler, moncler outlet, louis vuitton, moncler outlet, links of london, ugg,uggs,uggs canada, montre pas cher, louis vuitton, nike air max, lancel, converse, swarovski crystal, moncler, juicy couture outlet, juicy couture outlet, moncler uk, canada goose jackets, ugg pas cher, moncler, pandora jewelry, swarovski, gucci, ugg, vans, hollister, louis vuitton, louis vuitton, karen millen uk, canada goose outlet, marc jacobs, canada goose, supra shoes, louis vuitton, thomas sabo, ugg,ugg australia,ugg italia, pandora uk, barbour uk, pandora jewelry, moncler, converse outlet, ray ban, moncler, canada goose


Post a Comment

Links to this post:

Create a Link

<< Home