Re: FW: OSPF Metric of > 65535??? WTF!

Thanks Bob - you just can't argue with proof by IOS / debug!!!

Thanks
Larry Hadrava
CCIE #12203
Check Out MyBlog: http://ccie12203.wordpress.com/

On Tue, Oct 19, 2010 at 2:42 PM, Bob Sinclair <bob_at_bobsinclair.net> wrote:

> Hi Mike,
>
> I think you will find that the maximum OSPF metric is actually 2^24. This
> is the size of the metric field in the LSA.
>
> R5(config-router)#default-metric ?
> <1-16777214> OSPF default metric
>
> Above shows maximum metric that can still be advertised. BTW; a metric of
> 0 will also be advertised.
>
> Turn on debug ip ospf lsa-generation, kill an external route, and you will
> see the LSA is withdrawn by advertising the poisoned metric, 16777215
>
> R1#debug ip osp lsa-generation
> OSPF summary lsa generation debugging is on
> R1#
> *Oct 19 18:47:02.867: BGP(0): route 158.10.107.0/24 modified
> *Oct 19 18:47:02.991: OSPF: Generate external LSA 158.10.107.0, mask
> 255.255.255.0, type 5, age 3600, metric 16777215, tag 0, metric-type 2, seq
> 0x80000005
>
> HTH,
>
> Bob Sinclair CCIE 10427 CCSI 30427
> CIERS2 Online Instructor
> www.tinyurl.com/ciers2online
>
>
>
> > -----Original Message-----
> > From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of
> > Mike Kiefer
> > Sent: Tuesday, October 19, 2010 1:47 PM
> > To: ccielab_at_groupstudy.com
> > Subject: OSPF Metric of > 65535??? WTF!
> >
> > I was always under the impression the maximum metric of OSPF is 65535.
> > Anything beyond that wouldn't make it into the routing table. The
> > behavior
> > would be similar to a RIP route with a hop count of 16 that's
> > considered
> > unreachable.
> >
> > I noticed a few routes on our production network that exceeded 65535
> > mainly
> > because of network engineer stupidity.
> >
> > So I made a real simple lab in GNS3. R1 connects to R2 connects to R3.
> > R1, R2,
> > and R3 have 1.1.1.1, 2.2.2.2, and 3.3.3.3 as loopbacks and all of the
> > links
> > are maxed out with ip ospf cost 65535.
> >
> >
> > R1(config-if)#do sh ip route
> > Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
> > D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
> > N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
> > E1 - OSPF external type 1, E2 - OSPF external type 2
> > i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS
> > level-2
> > ia - IS-IS inter area, * - candidate default, U - per-user
> > static
> > route
> > o - ODR, P - periodic downloaded static route
> >
> > Gateway of last resort is not set
> >
> > 1.0.0.0/32 is subnetted, 1 subnets
> > C 1.1.1.1 is directly connected, Loopback0
> > 2.0.0.0/32 is subnetted, 1 subnets
> > O IA 2.2.2.2 [110/131070] via 12.1.1.2, 00:07:10, FastEthernet0/0
> > 3.0.0.0/32 is subnetted, 1 subnets
> > O IA 3.3.3.3 [110/196605] via 12.1.1.2, 00:02:11, FastEthernet0/0
> > 12.0.0.0/24 is subnetted, 1 subnets
> > C 12.1.1.0 is directly connected, FastEthernet0/0
> > 13.0.0.0/24 is subnetted, 1 subnets
> > O 13.1.1.0 [110/131070] via 12.1.1.2, 00:02:21, FastEthernet0/0
> >
> >
> > R1(config-if)#do sh ip ospf data summ
> >
> > OSPF Router with ID (1.1.1.1) (Process ID 1)
> >
> > Summary Net Link States (Area 0)
> >
> > Routing Bit Set on this LSA
> > LS age: 654
> > Options: (No TOS-capability, DC, Upward)
> > LS Type: Summary Links(Network)
> > Link State ID: 2.2.2.2 (summary Network Number)
> > Advertising Router: 2.2.2.2
> > LS Seq Number: 80000002
> > Checksum: 0xEE3D
> > Length: 28
> > Network Mask: /32
> > TOS: 0 Metric: 65535
> >
> > Routing Bit Set on this LSA
> > LS age: 471
> > Options: (No TOS-capability, DC, Upward)
> > LS Type: Summary Links(Network)
> > Link State ID: 3.3.3.3 (summary Network Number)
> > Advertising Router: 3.3.3.3
> > LS Seq Number: 80000001
> > Checksum: 0xA480
> > Length: 28
> > Network Mask: /32
> > TOS: 0 Metric: 65535
> >
> > How do I get a routing metric > 65535? Why are both 2.2.2.2 and 3.3.3.3
> > only
> > showing 65535 in the DB and higher metrics in the routing table? Isn't
> > the
> > 65535 based on the fact that there are only 16 bits for metric?
> >
> > What gives???
> >
> >
> > Blogs and organic groups at http://www.ccie.net
> >
> > _______________________________________________________________________
> > Subscription information may be found at:
> > http://www.groupstudy.com/list/CCIELab.html
> >
> >
> >
> >
> >
> >
> >
> > No virus found in this incoming message.
> > Checked by AVG - www.avg.com
> > Version: 9.0.862 / Virus Database: 271.1.1/3206 - Release Date:
> > 10/19/10 02:34:00
>
>
> Blogs and organic groups at http://www.ccie.net
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html

Blogs and organic groups at http://www.ccie.net
Received on Tue Oct 19 2010 - 14:57:07 ART