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

davischw · 2025-02-11T14:01:04Z

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

riw777

looks good

donaldsharp · 2025-02-11T15:53:42Z

NAK - PUT THE ANALYSIS IN THE COMMIT MESSAGE

donaldsharp

NAK

davischw · 2025-02-11T16:12:39Z

@donaldsharp

Do you have any technical reasons for NAKing this or is it just cosmetic things (commit message, comments in code, variable names)?

donaldsharp · 2025-02-11T16:16:43Z

This is a technical reason. No commit messages are technically useless to developers several years from now when they are looking at code.

davischw · 2025-02-13T14:18:44Z

@donaldsharp I think i addressed the changes requested by you in my latest code push. You happy?

donaldsharp · 2025-02-13T18:58:38Z

why is this a draft?

davischw · 2025-02-14T11:35:33Z

@donaldsharp

why is this a draft?

Not anymore. Let me fix the detected styling issues before you pressing the merge button, though.

Changes allow ipv4 class E addresses and prefixes in the 240.0.0.0/4 range to be configured on interfaces, imported from the kernel routing table and redistributed as connected routes in zebra by default. Changes also fix routes with class E prefixes in kernel routing table getting rejected by zebra during early daemon startup. Drivin this change in default behavior 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. Signed-off-by: David Schweizer <dschweizer@opensourcerouting.org>

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>

olivettiwetti

I can confirm that this change fixes the problem on our systems, thank you very much.

davischw · 2025-02-17T07:20:00Z

@donaldsharp Merge?

mwinter-osr · 2025-07-10T22:05:51Z

@Mergifyio backport dev/10.4

mergify · 2025-07-10T22:05:59Z

backport dev/10.4

✅ Backports have been created

#19175 Use ipv4 class E addresses (240.0.0.0/4) as connected routes by default (backport #18095) has been created for branch dev/10.4 but encountered conflicts

mwinter-osr · 2025-07-10T22:07:38Z

@Mergifyio backport stable/10.3

mergify · 2025-07-10T22:07:46Z

backport stable/10.3

✅ Backports have been created

#19176 Use ipv4 class E addresses (240.0.0.0/4) as connected routes by default (backport #18095) has been created for branch stable/10.3

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

* bgpd: correct no form commands (backport FRRouting#18911) * bgpd: fix to show exist/non-exist-map in 'show run' properly FRRouting#18853 * redhat: make FRR RPM build to work on RedHat 10 (backport FRRouting#18920) * build: check for libunwind.h, not unwind.h (backport FRRouting#18912) * bgpd: use AS4B format for BGP loc-rib messages. (backport FRRouting#18936) * bgpd: fix for the validity and the presence of prefixes in the BGP VPN table. (backport FRRouting#17370) * bgpd: Force adj-rib-out updates if MRAI is kicked in (backport FRRouting#18959) * zebra: Provide SID value when sending SRv6 SID release notify message (backport FRRouting#18971) * bgpd: Fix crash when fetching statistics for bgp instance (backport FRRouting#19003) * nhrpd: fix crash when accessing invalid memory zone (backport FRRouting#18994) * zebra: Initialize RB tree for router tables (backport FRRouting#19049) * zebra: fix null pointer dereference in zebra_evpn_sync_neigh_del (backport FRRouting#19054) * zebra: fix stale NHG in kernel (backport FRRouting#18899) * bgpd: Fix incorrect stripping of transitive extended communities (backport FRRouting#19065) * lib: Fix no on-match goto NUM command (backport FRRouting#19108) * bgpd: Fix extended community check for IP non-transitive type (backport FRRouting#19097) * bgpd: Fix DEREF_OF_NULL.EX.COND in bgp_updgrp_packet (backport FRRouting#19126) * lib: revert addition of vtysh_flush() call in vty_out() (backport FRRouting#19109) * bgpd: Extract link bandwidth value from extcommunity before using for WCMP (backport FRRouting#19165) * Use ipv4 class E addresses (240.0.0.0/4) as connected routes by default (backport FRRouting#18095) * bfdd: Set bfd.LocalDiag when transitioning to AdminDown (backport FRRouting#18592) * zebra: clean up a json object leak (backport FRRouting#19192) * bgpd: Do not try to reuse freed route-maps (backport FRRouting#19191) * lib: fix routemap crash (backport FRRouting#19127) * bgpd: initialize local variable (backport FRRouting#19233) * ospfd: Use after free cleanup of lsa (backport FRRouting#19224) * vtysh: copy config from file should actually apply (backport FRRouting#19242) * bgpd : Fix compilation error in bgpd module: Update TP_ARGS for bgp (backport FRRouting#19266) * bgpd: Ensure addpath does not withdraw selected route in some situations (backport FRRouting#19210) * lib, zebra: mark singleton nexthops inactive/active on link state changes for wecmp (backport FRRouting#18947) * eigrp: validate hello packets and tlvs better (backport FRRouting#19251) * bgpd: [GR] fixed selectionDeferralTimer to display select_defer_time val FRRouting#19283 Signed-off-by: Donatas Abraitis <donatas@opensourcerouting.org>

frrbot bot added libfrr zebra labels Feb 11, 2025

github-actions bot added master size/S labels Feb 11, 2025

riw777 self-requested a review February 11, 2025 15:32

riw777 approved these changes Feb 11, 2025

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donaldsharp self-requested a review February 11, 2025 15:55

donaldsharp requested changes Feb 11, 2025

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davischw changed the title ~~Use ipv4 class E addresses (240.0.0.0/8) as connected routes by default~~ Use ipv4 class E addresses (240.0.0.0/4) as connected routes by default Feb 12, 2025

davischw force-pushed the zebra-check-class-e branch from 6bdf47e to 3da8838 Compare February 12, 2025 12:25

frrbot bot added the documentation label Feb 12, 2025

davischw requested a review from donaldsharp February 12, 2025 13:03

donaldsharp approved these changes Feb 13, 2025

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davischw marked this pull request as ready for review February 14, 2025 11:31

davischw added 2 commits February 14, 2025 15:05

doc: Update description of 'allow-reserved-ranges'

1951e71

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>

davischw force-pushed the zebra-check-class-e branch from 3da8838 to 1951e71 Compare February 14, 2025 14:06

olivettiwetti reviewed Feb 14, 2025

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riw777 merged commit 3eedab0 into FRRouting:master Feb 18, 2025
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olivettiwetti mentioned this pull request Feb 19, 2025

A restart of FRR does not configure the loopback class E address if it already exists #16326

Closed

github-actions bot added the backport label Jul 10, 2025

mergify bot mentioned this pull request Jul 10, 2025

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

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mergify bot mentioned this pull request Jul 10, 2025

Use ipv4 class E addresses (240.0.0.0/4) as connected routes by default (backport #18095) #19176

Merged

ton31337 added a commit that referenced this pull request Jul 11, 2025

Merge pull request #19176 from FRRouting/mergify/bp/stable/10.3/pr-18095

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

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