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Use ipv4 class E addresses (240.0.0.0/4) as connected routes by default (backport #18095) #19175

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Use ipv4 class E addresses (240.0.0.0/4) as connected routes by default (backport #18095) #19175

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@mergify mergify bot commented Jul 10, 2025

Changes allow ipv4 class E addresses in the 240.0.0.0/4 range to be displayed and used as connected routes in zebra by default.

Reason for changes are cloud providers (with customers still using obsolete ipv4 protocol, i.e. Azure, AWS) running out of ip space and abusing class E for addressing instances (announced via BGP) over tunneling connections back to customers on premise infrastructure.

Kernel routing table:

root@frr:~# ip route
default via 192.168.1.1 dev enp10s0 
192.168.1.0/24 dev enp10s0 proto kernel scope link src 192.168.1.111
192.168.122.0/24 dev enp9s0 proto kernel scope link src 192.168.122.253
240.12.12.0/24 dev enp1s0 proto kernel scope link src 240.12.12.12 <---
240.80.45.0/24 dev enp1s0 proto kernel scope link src 240.80.45.1 <---

Without patch:

frr# show ip route
Codes: K - kernel route, C - connected, L - local, S - static,
       R - RIP, O - OSPF, I - IS-IS, B - BGP, E - EIGRP, N - NHRP,
       T - Table, v - VNC, V - VNC-Direct, A - Babel, D - SHARP,
       F - PBR, f - OpenFabric, t - Table-Direct,
       > - selected route, * - FIB route, q - queued, r - rejected, b - backup
       t - trapped, o - offload failure

IPv4 unicast VRF default:
K>* 0.0.0.0/0 [0/0] via 192.168.1.1, enp10s0, weight 1, 00:00:14
C>* 192.168.1.0/24 is directly connected, enp10s0, weight 1, 00:00:14
L>* 192.168.1.111/32 is directly connected, enp10s0, weight 1, 00:00:14
C>* 192.168.122.0/24 is directly connected, enp9s0, weight 1, 00:00:14
L>* 192.168.122.253/32 is directly connected, enp9s0, weight 1, 00:00:14
K>* 240.12.12.0/24 [0/0] is directly connected, enp1s0, weight 1, 00:00:14 <---
K>* 240.80.45.0/24 [0/0] is directly connected, enp1s0, weight 1, 00:00:14 <---

With patch:

frr# show ip route
Codes: K - kernel route, C - connected, L - local, S - static,
       R - RIP, O - OSPF, I - IS-IS, B - BGP, E - EIGRP, N - NHRP,
       T - Table, v - VNC, V - VNC-Direct, A - Babel, D - SHARP,
       F - PBR, f - OpenFabric, t - Table-Direct,
       > - selected route, * - FIB route, q - queued, r - rejected, b - backup
       t - trapped, o - offload failure

IPv4 unicast VRF default:
K>* 0.0.0.0/0 [0/0] via 192.168.1.1, enp10s0, weight 1, 00:00:16
C>* 192.168.1.0/24 is directly connected, enp10s0, weight 1, 00:00:16
L>* 192.168.1.111/32 is directly connected, enp10s0, weight 1, 00:00:16
C>* 192.168.122.0/24 is directly connected, enp9s0, weight 1, 00:00:16
L>* 192.168.122.253/32 is directly connected, enp9s0, weight 1, 00:00:16
C>* 240.12.12.0/24 is directly connected, enp1s0, weight 1, 00:00:16 <---
L>* 240.12.12.12/32 is directly connected, enp1s0, weight 1, 00:00:16 <---
C>* 240.80.45.0/24 is directly connected, enp1s0, weight 1, 00:00:16 <---
L>* 240.80.45.1/32 is directly connected, enp1s0, weight 1, 00:00:16 <---

Related issues:
#16326
#17942

This is an automatic backport of pull request #18095 done by Mergify.

@davischw @mergify
doc: Update description of 'allow-reserved-ranges'
e0ce1b4 
Update user documentation to reflect behavior of config command
'allow-reserved-ranges' after changes enable use of ipv4 class E
addresses by default.

Signed-off-by: David Schweizer <dschweizer@opensourcerouting.org>
(cherry picked from commit 1951e71)

# Conflicts:
#	doc/user/basic.rst
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mergify bot commented Jul 10, 2025

Cherry-pick of 1951e71 has failed:

On branch mergify/bp/dev/10.4/pr-18095
Your branch is up to date with 'origin/dev/10.4'.

You are currently cherry-picking commit 1951e713d.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   doc/user/basic.rst

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

@mergify mergify bot added the conflicts label Jul 10, 2025
@mergify mergify bot mentioned this pull request Jul 10, 2025
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@frrbot frrbot bot added the documentation label Jul 10, 2025
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Wrong backport branch... closing it. 10.4 already has this

@Jafaral Jafaral deleted the mergify/bp/dev/10.4/pr-18095 branch July 31, 2025 15:03
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