IS-IS Redistribution: Route not withdrawn from LSP after prefix-list change
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	c.faria
	May 15 2026, 10:13 AM

Description

When a prefix is removed from a prefix-list used in IS-IS redistribution, the IS-IS daemon does not trigger a redistribution update to withdraw the route from the LSP. The stale route remains in the LSP and continues to be propagated throughout the IS-IS domain until a redistribution recalculation is manually forced. This behavior was reproduced in the lab environment running VyOS 1.4.4 with FRR 9.1.3.

###Environment###
VyOS Version1.4.4
FRR Version 9.1.3
IS-IS Level Level-2
Metric Style Wide
Redistribution IPv4 static - IS-IS level-2 via route-map

###Lab Topology###
2x VyOS routers, point-to-point eth1 <-> eth1
Router ALAB-CORE-01 | lo: 192.0.2.1/32 | eth1: 198.51.100.1/31
Router BLAB-EDGE-01 | lo: 192.0.2.2/32 | eth1: 198.51.100.0/31

###Steps to Reproduce###
###LAB-CORE-01###
# Interfaces
set interfaces ethernet eth1 address '198.51.100.1/31'
set interfaces ethernet eth1 description 'LAB-CORE-01-LAB-EDGE-01'
set interfaces loopback lo address '192.0.2.1/32'
set interfaces loopback lo description 'LOOPBACK'

# Static routes
set protocols static route 203.0.113.0/28 next-hop '198.51.100.0'
set protocols static route 203.0.113.16/28 next-hop '198.51.100.0'
set protocols static route 203.0.113.32/32 next-hop '198.51.100.0'

# Prefix-list
set policy prefix-list REDISTRIBUTE_ISIS rule 10 action permit
set policy prefix-list REDISTRIBUTE_ISIS rule 10 prefix 203.0.113.0/28
set policy prefix-list REDISTRIBUTE_ISIS rule 20 action permit
set policy prefix-list REDISTRIBUTE_ISIS rule 20 prefix 203.0.113.16/28
set policy prefix-list REDISTRIBUTE_ISIS rule 30 action permit
set policy prefix-list REDISTRIBUTE_ISIS rule 30 prefix 203.0.113.32/32

# Route-map
set policy route-map REDISTRIBUTE-ISIS rule 10 action permit
set policy route-map REDISTRIBUTE-ISIS rule 10 match ip address prefix-list REDISTRIBUTE_ISIS
set policy route-map REDISTRIBUTE-ISIS rule 100 action deny

# IS-IS
set protocols isis net '49.0001.1920.0200.0001.00'
set protocols isis level 'level-2'
set protocols isis metric-style 'wide'
set protocols isis dynamic-hostname
set protocols isis log-adjacency-changes
set protocols isis interface eth1 metric '10'
set protocols isis interface eth1 network point-to-point
set protocols isis interface lo passive
set protocols isis interface lo metric '10'

# IS-IS redistribution
set protocols isis redistribute ipv4 static level-2 route-map 'REDISTRIBUTE-ISIS'

# BGP
set protocols bgp system-as '64512'
set protocols bgp parameters router-id '192.0.2.1'
set protocols bgp neighbor 192.0.2.2 remote-as '64512'
set protocols bgp neighbor 192.0.2.2 description 'LAB-EDGE-01'
set protocols bgp neighbor 192.0.2.2 update-source 'lo'
set protocols bgp neighbor 192.0.2.2 address-family ipv4-unicast nexthop-self

# System
set system host-name 'LAB-CORE-01'
commit
save


###LAB-EDGE-01###
# Interfaces
set interfaces ethernet eth1 address '198.51.100.0/31'
set interfaces ethernet eth1 description 'LAB-EDGE-01-LAB-CORE-01'
set interfaces loopback lo address '192.0.2.2/32'
set interfaces loopback lo description 'LOOPBACK'

# Route-map
set policy route-map ALLOW-ALL rule 10 action permit

# IS-IS
set protocols isis net '49.0001.1920.0200.0002.00'
set protocols isis level 'level-2'
set protocols isis metric-style 'wide'
set protocols isis dynamic-hostname
set protocols isis log-adjacency-changes
set protocols isis interface eth1 metric '10'
set protocols isis interface eth1 network point-to-point
set protocols isis interface lo passive
set protocols isis interface lo metric '10'

# BGP
set protocols bgp system-as '64512'
set protocols bgp parameters router-id '192.0.2.2'
set protocols bgp neighbor 192.0.2.1 remote-as '64512'
set protocols bgp neighbor 192.0.2.1 description 'LAB-CORE-01'
set protocols bgp neighbor 192.0.2.1 update-source 'lo'
set protocols bgp neighbor 192.0.2.1 address-family ipv4-unicast nexthop-self
set protocols bgp neighbor 192.0.2.1 address-family ipv4-unicast route-map import 'ALLOW-ALL'

# System
set system host-name 'LAB-EDGE-01'

Verify prefixes are redistributed into IS-IS

LAB-CORE-01
LAB-CORE-01# run show isis database detail

Extended IP Reachability: 203.0.113.0/28  (Metric: 0)
Extended IP Reachability: 203.0.113.16/28 (Metric: 0)
Extended IP Reachability: 203.0.113.32/32 (Metric: 0)

LAB-EDGE-01
LAB-EDGE-01# run show ip route isis
I>* 203.0.113.0/28 [115/10] via 198.51.100.1, eth1, weight 1
I>* 203.0.113.16/28 [115/10] via 198.51.100.1, eth1, weight 1
I>* 203.0.113.32/32 [115/10] via 198.51.100.1, eth1, weight 1

Remove a prefix from the prefix-list

LAB-CORE-01
delete policy prefix-list REDISTRIBUTE_ISIS rule 20
commit
save

Verify the prefix-list change was applied

LAB-CORE-01
LAB-CORE-01# run show ip prefix-list REDISTRIBUTE_ISIS
ISIS: ip prefix-list REDISTRIBUTE_ISIS: 2 entries

seq 10 permit 203.0.113.0/28
seq 30 permit 203.0.113.32/32
###seq 20 permit 203.0.113.16/28###  ###no longer present###

Observed Behavior

Despite the prefix 203.0.113.16/28 being removed from the prefix-list and the change confirmed in the output above, the IS-IS LSP on LAB-CORE-01 continues to advertise the prefix with Metric: 0:
LAB-CORE-01ALAB-CORE-01# run show isis database detail
LAB-CORE-01.00-00 *

...
Extended IP Reachability: 203.0.113.0/28  (Metric: 0)
Extended IP Reachability: 203.0.113.16/28 (Metric: 0)  ###still present###
Extended IP Reachability: 203.0.113.32/32 (Metric: 0)

The prefix continues to be propagated to all IS-IS neighbors:

LAB-EDGE-01# run show ip route 203.0.113.16/28
Routing entry for 203.0.113.16/28

Known via "isis", distance 115, metric 10, best
Last update 00:22:32 ago
* 198.51.100.1, via eth1, weight 1

Expected Behavior

When a prefix is removed from the prefix-list and the change is committed, the IS-IS daemon should immediately trigger a redistribution update to withdraw the route from the LSP. Expected output after removing rule 20:
LAB-CORE-01# run show isis database detail
LAB-CORE-01.00-00 *

...
Extended IP Reachability: 203.0.113.0/28  (Metric: 0)
Extended IP Reachability: 203.0.113.32/32 (Metric: 0)
###203.0.113.16/28 should NOT be present###

Validated Workaround

delete protocols isis redistribute
commit
set protocols isis redistribute ipv4 static level-2 route-map REDISTRIBUTE-ISIS
commit
save

Details

Version: 1.4.4
Is it a breaking change?: Perfectly compatible
Issue type: Bug (incorrect behavior)

Event Timeline

c.faria created this task.May 15 2026, 10:13 AM

c.faria triaged this task as Normal priority.

c.faria created this object in space S1 VyOS Public.

c.faria created this object with edit policy "All Users".

samuel.menon subscribed.May 26 2026, 5:42 PM

IS-IS Redistribution: Route not withdrawn from LSP after prefix-list changeOpen, NormalPublicActions