what does the function of the TLV 132 in LSP ?

[wlsj]

In ISIS protocol,what is the function of the TLV 132 in LSP? It seems like routers choose the latest active interface on the box,is it right ?

[Giuseppe Larosa]

Hello WL,

the TLV lists the ip addresses of the interface out which the isis LSP is sent:

if the ipv4 address listed in TLV 132 doesn't match, it isn't in the same IP subnet, that of the receiving interface a clns adjacency is established but not shown as L1 or L2.

This is useful because IS-IS use its own packets and ipv4 addresses are seen as leaf attributes.

the IS-IS router-id is actually provided by the net command + system-id and it is a CLNS address.

Hope to help

Giuseppe

[wlsj]

do you mean the TLV 132 in hello packet? but i do not know what is the function of TLV132 in LSP?

[Giuseppe Larosa]

Hello WL,

the TLV 132 is present in hello packets but also on the LSP both L1 and L2 and contains the ip address(es) of the transmitting interface

As explained in the previous post this TLV allows the receiving router(s) to perform a check of adjancency validity from the point of view of IPv4.

Probably the TLV 132 is present in the LSP for two reasons:

for completeness and for providing a fast check about the usage of the LSP.

The LSP indeed is a list of TLVs so implementation can also be a little redundant here by putting all TLVs into the LSP.

This also means that the LSP sent out each interface is different in TLV 132 field.

You can see with sh isis database detail that each LSP contains a list of IP subnets and associated metric costs this can come from a list of TLV 132.

TLV 128-132 are defined in RFC1195 for IP routing with IS-IS.

IP Interface Address -- the IP address(es) of the interface

corresponding to the SNPA over which this PDU is to be transmitted.

x CODE - 132

x LENGTH - total length of the value field (four octets per address).

x VALUE -

It is TLV 128 that provides metric info for IP.

Hope to help

Giuseppe

[wlsj]

Hi, The TLV 132 in hello and LSP are different;in hello packet,it is the related subnet,but in LSP,it is the latest active ISIS interface;what do you think?

[Giuseppe Larosa]

Hello WL,

I made a search in RFC 1195 in all cases where the TLV 132 appears it is stated that it represents the ip address(es) of the transmitting interface.

see

http://www.faqs.org/rfcs/rfc1195.html

see paragraphs 5.3.1 -5.3.3 for the hellos PDUs

have you made a packet capture of IS-IS messages ?

I also don't understand what you mean with the latest active IS-IS interface.

However, we have a production network with more then two hundreds of routers running IS-IS next week I'll see if I can try to setup a packet capture with a SPAN session.

Hope to help

Giuseppe

[wlsj]

this packet is captured by wireshark,the TLV 132 in hello and LSP are different

[lgrzesiowski]

In Link state PDU TLV 132 lists all IP addressess configured on the local router - at least one router interface must be advertised. By default when Junos sends LSP PDU it pupulates TLV 132 with router ID of the local router, which is usually primary ip address configured on lo0 interface. I belive, that in Cisco it works in similar manner. So concluded - in IIH PDU and LSP PDU TLV 132 convey different IP addressess.