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net/ipforward: Forbid non-forwardable multicast scopes. #18738

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Merged
acassis merged 1 commit into from
Apr 18, 2026
+23 −0
Merged

net/ipforward: Forbid non-forwardable multicast scopes. #18738

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12 changes: 12 additions & 0 deletions net/ipforward/ipv4_forward.c
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Original file line number Diff line number Diff line change
Expand Up @@ -634,6 +634,18 @@ void ipv4_forward_broadcast(FAR struct net_driver_s *dev,
return;
}

/* Do not forward link-local multicast packets (224.0.0.0/24).
* Per RFC 3171, addresses in 224.0.0.0/24 are reserved for
* link-local scope and MUST NOT be forwarded by any router,
* regardless of TTL.
*/

if ((net_ip4addr_conv32(ipv4->destipaddr) &
HTONL(0xffffff00)) == HTONL(0xe0000000))
{
return;
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}

/* Don't bother if the TTL would expire */

if (ipv4->ttl > 1)
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11 changes: 11 additions & 0 deletions net/ipforward/ipv6_forward.c
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Original file line number Diff line number Diff line change
Expand Up @@ -810,6 +810,17 @@ void ipv6_forward_broadcast(FAR struct net_driver_s *dev,
return;
}

/* Do not forward reserved, interface-local, or link-local multicast
* destinations (ffx0::/16, ffx1::/16, ffx2::/16).
*/

if (((ipv6->destipaddr[0] & HTONS(0xff0f)) == HTONS(0xff00)) ||
((ipv6->destipaddr[0] & HTONS(0xff0f)) == HTONS(0xff01)) ||
((ipv6->destipaddr[0] & HTONS(0xff0f)) == HTONS(0xff02)))
{
return;
}

/* Don't bother if the TTL would expire */

if (ipv6->ttl > 1)
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