Re: OSPF LSA type 3 filtering

For ISIS, you could have used the "clns mtu" command to fix it instead of
changing the MTU under the interface. Padding in ISIS can also be disabled but
it will still pad the first 5 hello's to ensure there is no mismatch.

Paul Negron
CCIE# 14856
negron.paul_at_gmail.com
303-725-8162

On Jan 5, 2013, at 12:17 PM, John Neiberger <jneiberger_at_gmail.com> wrote:

> I ran into that ISIS MTU issue at work this week on a production link. I
needed to increase the MTU on a link that was running OSPF and ISIS. When I
changed the MTU on one side, ISIS got a little angry with me until I increased
the MTU on the other side. The reason is that ISIS has a Padding TLV wherein
it pads its hello packets to the full MTU size. That's how it insures that
there is no mismatch. If one side has a larger MTU, that packet will be
dropped when it reaches the other side. Once I fixed both ends, ISIS was happy
again.
>
> Interestingly, OSPF also bounced, which I thought was odd. In IOS, if you
already have an adjacency and routing is stable, you can change the MTU
without causing the adjacency to bounce. However, I was doing this in IOS XR
and it clearly bounced OSPF when I changed the MTU. I asked around on the
cisco-nsp list, but so far no one knows why OSPF would bounce like that in IOS
XR. One person thought that perhaps since it is a hardware forwarding
platform, interface buffer memory had to be reallocated after the MTU change,
but that was just a guess. If anyone knows, feel free to end the mystery. lol
I know it won't bounce the adjacency in IOS, at least on the hardware and
images I tested it on. And that makes sense to me. The MTU is not in the hello
packets in OSPF; it's in the DBD packets.
>
> John
>
>
> On Fri, Jan 4, 2013 at 7:14 PM, Paul Negron <negron.paul_at_gmail.com> wrote:
> I do like that feature.
>
> I also love the way ISIS handles MTU mismatch which is another big problem
we
> have in real networks.
> You do not just simply ignore it as you do with OSPF.
>
> Paul
> Paul Negron
> CCIE# 14856
> negron.paul_at_gmail.com
>
>
> On Jan 4, 2013, at 1:17 PM, Yuri Bank <yuribank_at_gmail.com> wrote:
>
> > Except that with the IS-IS the hostname is carried in each routers LSP
> > (hostname TLV), so there is no dependency on DNS, or manual configuration
> > on the routers required (Which is very nice imho).
> >
> > -Yuri
> >
> >
> > On Fri, Jan 4, 2013 at 12:10 PM, Marko Milivojevic
> <markom_at_ipexpert.com>wrote:
> >
> >> You mean the output you'd get if you used "ip ospf name-lookup" ;-)
> >>
> >> --
> >> Marko Milivojevic - CCIE #18427 (SP R&S)
> >> Senior CCIE Instructor - IPexpert
> >>
> >> On Fri, Jan 4, 2013 at 12:07 PM, rakesh madupu <raaki.88_at_gmail.com>
wrote:
> >>> For me, I love isis in our customer deployments because it shows
> >>> neighboring devices names which is peers with, specially with RR's
names
> >> ,
> >>> life get so much simpler instead of reading an Ip address and
> >> associating it
> >>> again :)
> >>>
> >>>
> >>> On Sat, Jan 5, 2013 at 12:34 AM, Marko Milivojevic
<markom_at_ipexpert.com>
> >>> wrote:
> >>>>
> >>>> IS-IS supports multiple routed protocols, i.e. IPv4 and IPv6, whereas
> >>>> OSPF doesn't.
> >>>>
> >>>> Also, in the time when MPLS-TE was emerging as a technology, IS-IS
> >>>> behavior to flood unknown TLVs instead of resetting adjacencies when
> >>>> it receives them (OSPF does that when it receives an unknown LSA).
> >>>> meant a very controlled deployment of new technologies. The fact it's
> >>>> not IP, also has some security benefits (cannot be remotely attacked).
> >>>> Etc.
> >>>>
> >>>> What Joseph said is... not quite the reason, since IS-IS also has a
> >>>> requirement for a contiguous L2 area.
> >>>>
> >>>> --
> >>>> Marko Milivojevic - CCIE #18427 (SP R&S)
> >>>> Senior CCIE Instructor - IPexpert
> >>>>
> >>>> On Fri, Jan 4, 2013 at 10:34 AM, Imran Ali <immrccie_at_gmail.com> wrote:
> >>>>> marko i need to know why they use is-is over ospf
> >>>>>
> >>>>> On Fri, Jan 4, 2013 at 8:53 PM, Marko Milivojevic <
> >> markom_at_ipexpert.com>
> >>>>> wrote:
> >>>>>>
> >>>>>> In reality, for this purpose, IS-IS and OSPF are pretty much the
same
> >>>>>> (Type 2 vs Pseudonode LSP). They both use a very similar approach to
> >>>>>> solve the same calculation problem.
> >>>>>>
> >>>>>> Carriers tend to use IS-IS for one other reason (to some extent
> >>>>>> remedied by OSPFv3). This is a separate discussion though.
> >>>>>>
> >>>>>> --
> >>>>>> Marko Milivojevic - CCIE #18427 (SP R&S)
> >>>>>> Senior CCIE Instructor - IPexpert
> >>>>>>
> >>>>>>
> >>>>>> 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 Sat Jan 05 2013 - 15:27:16 ART