Description

This article describes the issue of the wide-metric-only configuration not changing the type of route for IPv6 external routes.

Symptoms

The wide-metric-only configuration does not change the route type for IPv6 external routes.

Solution


For IPv4, TLV 128 (internal) and 130 (external) are used for route advertisement. With wide-metric-only being configured, the router sends only TLV 135 and ignores the setting in TLV 128 and TLV 130 . TLV 135 does not have the bit to indicate an internal or external route. So, IPv4 external routes are also programmed as Internal in the ISIS database.

For IPv6, TLV 236 is present; which contains the Internal/External bit. When advertising the external route, it sets the external bit. The wide-metirc-only configuration does not affect the route type for IPv6. So, an external route will appear as External in the ISIS database.

Topology :

[lr2]--- [lr1]---[lr3]
  • lr2 has a static route, which is exported (policy) via ISIS.
  • Static route prefix - 2001:5e8:0:fe10::/128 .
  • On lr3, you can see the route as External, even after the wide-metric-only configuration.

Outputs :
lab@thepla-T1600-re0# run show route 2001:5e8:0:fe10::/128 logical-system lr3 detail

inet6.0: 13 destinations, 13 routes (13 active, 0 holddown, 0 hidden)
2001:5e8:0:fe10::/128 (1 entry, 1 announced)
*IS-IS Preference: 160
Level: 1
Next hop type: Router, Next hop index: 1079
Address: 0x8fa6250
Next-hop reference count: 12
Next hop: fe80::2e6b:f5ff:fee1:953b via ge-5/1/7.0, selected
State: <Active Int Ext>
Age: 1d 20:34:28 Metric: 120 <
Task: IS-IS
Announcement bits (1): 0-KRT
AS path: I

lab@thepla-T1600-re0# run show isis database detail logical-system lr1
IS-IS level 1 link-state database:

thepla-T1600-re0-lr2.00-00 Sequence: 0xb, Checksum: 0x5fb5, Lifetime: 980 secs
IS neighbor: thepla-T1600-re0-lr2.02 Metric: 10
V6 prefix: 2001:5e8:0:fe05::/64 Metric: 10 Internal Up
V6 prefix: 2001:5e8:0:fe06::20/127 Metric: 0 Internal Up
V6 prefix: 2001:5e8:0:fe06::20/128 Metric: 0 Internal Up
V6 prefix: 2001:5e8:0:fe10::/128 Metric: 0 External Up            <<<< Route shows up as External

thepla-T1600-re0-lr2.02-00 Sequence: 0xa, Checksum: 0x1cbe, Lifetime: 980 secs
IS neighbor: thepla-T1600-re0-lr2.00 Metric: 0
IS neighbor: thepla-T1600-re0-lr1.00 Metric: 0

thepla-T1600-re0-lr1.00-00 Sequence: 0x13, Checksum: 0xb3ae, Lifetime: 982 secs
IS neighbor: thepla-T1600-re0-lr2.02 Metric: 10
IS neighbor: thepla-T1600-re0-lr3.02 Metric: 10
V6 prefix: 2001:5e8:0:fe04::20/127 Metric: 0 Internal Up
V6 prefix: 2001:5e8:0:fe04::20/128 Metric: 0 Internal Up
V6 prefix: 2001:5e8:0:fe05::/64 Metric: 10 Internal Up
V6 prefix: 2001:5e8:0:fe07::/64 Metric: 10 Internal Up

thepla-T1600-re0-lr3.00-00 Sequence: 0x8, Checksum: 0xb448, Lifetime: 980 secs
IS neighbor: thepla-T1600-re0-lr3.02 Metric: 10
V6 prefix: 2001:5e8:0:fe07::/64 Metric: 10 Internal Up
V6 prefix: 2001:5e8:0:fe08::20/127 Metric: 0 Internal Up
V6 prefix: 2001:5e8:0:fe08::20/128 Metric: 0 Internal Up

thepla-T1600-re0-lr3.02-00 Sequence: 0x5, Checksum: 0x28b3, Lifetime: 980 secs
IS neighbor: thepla-T1600-re0-lr1.00 Metric: 0
IS neighbor: thepla-T1600-re0-lr3.00 Metric: 0

IS-IS level 2 link-state database:

[edit]
lab@thepla-T1600-re0# run show isis database detail logical-system lr2
IS-IS level 1 link-state database:

thepla-T1600-re0-lr2.00-00 Sequence: 0xb, Checksum: 0x5fb5, Lifetime: 980 secs
IS neighbor: thepla-T1600-re0-lr2.02 Metric: 10
V6 prefix: 2001:5e8:0:fe05::/64 Metric: 10 Internal Up
V6 prefix: 2001:5e8:0:fe06::20/127 Metric: 0 Internal Up
V6 prefix: 2001:5e8:0:fe06::20/128 Metric: 0 Internal Up
V6 prefix: 2001:5e8:0:fe10::/128 Metric: 0 External Up

thepla-T1600-re0-lr2.02-00 Sequence: 0xa, Checksum: 0x1cbe, Lifetime: 980 secs
IS neighbor: thepla-T1600-re0-lr2.00 Metric: 0
IS neighbor: thepla-T1600-re0-lr1.00 Metric: 0

thepla-T1600-re0-lr1.00-00 Sequence: 0x13, Checksum: 0xb3ae, Lifetime: 978 secs
IS neighbor: thepla-T1600-re0-lr2.02 Metric: 10
IS neighbor: thepla-T1600-re0-lr3.02 Metric: 10
V6 prefix: 2001:5e8:0:fe04::20/127 Metric: 0 Internal Up
V6 prefix: 2001:5e8:0:fe04::20/128 Metric: 0 Internal Up
V6 prefix: 2001:5e8:0:fe05::/64 Metric: 10 Internal Up
V6 prefix: 2001:5e8:0:fe07::/64 Metric: 10 Internal Up

thepla-T1600-re0-lr3.00-00 Sequence: 0x8, Checksum: 0xb448, Lifetime: 976 secs
IS neighbor: thepla-T1600-re0-lr3.02 Metric: 10
V6 prefix: 2001:5e8:0:fe07::/64 Metric: 10 Internal Up
V6 prefix: 2001:5e8:0:fe08::20/127 Metric: 0 Internal Up
V6 prefix: 2001:5e8:0:fe08::20/128 Metric: 0 Internal Up

thepla-T1600-re0-lr3.02-00 Sequence: 0x5, Checksum: 0x28b3, Lifetime: 976 secs
IS neighbor: thepla-T1600-re0-lr1.00 Metric: 0
IS neighbor: thepla-T1600-re0-lr3.00 Metric: 0

IS-IS level 2 link-state database:

[edit]
lab@thepla-T1600-re0# run show isis database detail logical-system lr3
IS-IS level 1 link-state database:

thepla-T1600-re0-lr2.00-00 Sequence: 0xb, Checksum: 0x5fb5, Lifetime: 974 secs
IS neighbor: thepla-T1600-re0-lr2.02 Metric: 10
V6 prefix: 2001:5e8:0:fe05::/64 Metric: 10 Internal Up
V6 prefix: 2001:5e8:0:fe06::20/127 Metric: 0 Internal Up
V6 prefix: 2001:5e8:0:fe06::20/128 Metric: 0 Internal Up
V6 prefix: 2001:5e8:0:fe10::/128 Metric: 0 External Up

thepla-T1600-re0-lr2.02-00 Sequence: 0xa, Checksum: 0x1cbe, Lifetime: 974 secs
IS neighbor: thepla-T1600-re0-lr2.00 Metric: 0
IS neighbor: thepla-T1600-re0-lr1.00 Metric: 0

thepla-T1600-re0-lr1.00-00 Sequence: 0x13, Checksum: 0xb3ae, Lifetime: 976 secs
IS neighbor: thepla-T1600-re0-lr2.02 Metric: 10
IS neighbor: thepla-T1600-re0-lr3.02 Metric: 10
V6 prefix: 2001:5e8:0:fe04::20/127 Metric: 0 Internal Up
V6 prefix: 2001:5e8:0:fe04::20/128 Metric: 0 Internal Up
V6 prefix: 2001:5e8:0:fe05::/64 Metric: 10 Internal Up
V6 prefix: 2001:5e8:0:fe07::/64 Metric: 10 Internal Up

thepla-T1600-re0-lr3.00-00 Sequence: 0x8, Checksum: 0xb448, Lifetime: 978 secs
IS neighbor: thepla-T1600-re0-lr3.02 Metric: 10
V6 prefix: 2001:5e8:0:fe07::/64 Metric: 10 Internal Up
V6 prefix: 2001:5e8:0:fe08::20/127 Metric: 0 Internal Up
V6 prefix: 2001:5e8:0:fe08::20/128 Metric: 0 Internal Up

thepla-T1600-re0-lr3.02-00 Sequence: 0x5, Checksum: 0x28b3, Lifetime: 978 secs
IS neighbor: thepla-T1600-re0-lr1.00 Metric: 0
IS neighbor: thepla-T1600-re0-lr3.00 Metric: 0
IS-IS level 2 link-state database:
[edit]
lab@thepla-T1600-re0#

Packet capture :
17:04:37.239419 In IS-IS, length 164
L1 LSP, hlen: 27, v: 1, pdu-v: 1, sys-id-len: 6 (0), max-area: 3 (0)
lsp-id: 1921.6800.0001.00-00, seq: 0x0000000b, lifetime: 1196s
chksum: 0x5fb5 (correct), PDU length: 164, Flags: [ L1 IS ]
Area address(es) TLV #1, length: 4
Area address (length: 3): 49.0002
Protocols supported TLV #129, length: 2
NLPID(s): IPv4 (0xcc), IPv6 (0x8e)
Hostname TLV #137, length: 20
Hostname: thepla-T1600-re0-lr2
Extended IS Reachability TLV #22, length: 21
IS Neighbor: 1921.6800.0001.02, Metric: 10, sub-TLVs present (10)
Link Local/Remote Identifier subTLV #4, length: 8, 0x0000005b, 0x00000000
IPv6 reachability TLV #236, length: 80 < IPv6 TLV
IPv6 prefix: 2001:5e8:0:fe05::/64, Distribution: up, Metric: 10, Internal
IPv6 prefix: 2001:5e8:0:fe06::20/128, Distribution: up, Metric: 0, Internal
IPv6 prefix: 2001:5e8:0:fe06::20/127, Distribution: up, Metric: 0, Internal
IPv6 prefix: 2001:5e8:0:fe10::/128, Distribution: up, Metric: 0, External