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[multicast] prevent VLAN translation via match key enforcement#195

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zeeshanlakhani wants to merge 8 commits intomainfrom
vlan-translation
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[multicast] prevent VLAN translation via match key enforcement#195
zeeshanlakhani wants to merge 8 commits intomainfrom
vlan-translation

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@zeeshanlakhani zeeshanlakhani commented Jan 22, 2026

This adds VLAN-aware NAT ingress matching to prevent cross-VLAN translation. Previously, a packet arriving with VLAN 100 destined to a multicast group configured for VLAN 200 would be NAT encapsulated and forwarded, effectively translating the packet to the wrong customer's network.

NAT ingress table matching (mcast_nat.rs, mod.rs):

  • Add Ipv4VlanMatchKey and Ipv6VlanMatchKey that match on destination address, VLAN header validity, and VLAN ID
  • Each group installs a single NAT entry with an exact VLAN match key. Decapsulated Geneve packets never reach the NatIngress tables (guarded by !hdr.geneve.isValid()), so a separate untagged entry is unnecessary.
  • Packets with the wrong VLAN miss the entry and are not NAT encapsulated

Multicast router VLAN handling (sidecar.p4):

  • forward_vlan(vlan_id) action re-adds the group's configured VLAN on egress
  • Fix MulticastRouter4 using IPv6 ICMP error codes (ICMP6_DST_UNREACH) instead of IPv4 (ICMP_DEST_UNREACH)

Rollback changes:

  • Remove dead NAT rollback branches for internal groups (no NAT entries)
  • Add rollback support for VLAN changes in NAT and route tables

…tering

Underlay changes:
- Restrict internal multicast from admin/site/org scoped (ff04, ff05, ff08)
  to just Omicron's reserved subnet (ff04::/64). These underlay addresses are
  made unique in Omicron.
- Rename `AdminScopedIpv6` to `UnderlayMulticastIpv6`.
- Simplify P4 to only match ff04::/64.
- Use omicron-common multicast constants for validation.

Source filtering changes:
- Replace IpSrc::Subnet with IpSrc::Any for any-source matching.
- Change IPv6 source filter from exact to LPM match.
- Allow source filters on ASM groups (previously SSM-only).

API changes:
- API v5 adds IpSrc::Any for ASM source filtering.
- API v6 enforces strict underlay subnet validation.
Fixes #107.

Stacked on #189.

This adds VLAN-aware NAT ingress matching to prevent cross-VLAN translation.
Previously, a packet arriving with VLAN 100 destined to a multicast group
configured for VLAN 200 would be NAT encapsulated and forwarded, effectively
translating the packet to the wrong customer's network.

NAT ingress table matching (mcast_nat.rs, mod.rs):
- Add Ipv4VlanMatchKey and Ipv6VlanMatchKey that match on destination address,
  VLAN header validity, and VLAN ID
- For groups with VLAN, install two entries: untagged (for decapsulated Geneve
  from underlay) and correctly tagged (for customer packets)
- Packets with the wrong VLAN miss both entries and are not NAT encapsulated

Multicast router VLAN handling (sidecar.p4):
- Strip incoming VLAN tag before routing lookup in MulticastRouter4/6
- forward_vlan action re-adds the group's configured VLAN on egress
- Prevents unintended VLAN translation at the routing stage

Rollback changes:
- Remove dead NAT rollback branches for internal groups (no NAT entries)
- Add rollback support for VLAN changes in NAT and route tables

Counter fix:
- The underlay multicast counter condition was unreachable for packets tagged
  MULTICAST_TAG_UNDERLAY_EXTERNAL that were not decapped. The check for
  == MULTICAST_TAG_UNDERLAY excluded these packets, causing them to fall
  through to the external counter.

Pull Request: #194
@zeeshanlakhani zeeshanlakhani self-assigned this Feb 19, 2026
…ation_ids

This includes some cleanup as well.
Base automatically changed from zl/admin-scope-oxnet to main February 26, 2026 12:07
Decapsulated Geneve packets never reach the NatIngress tables due to the
outermost !hdr.geneve.isValid() check, so the dual-entry approach (untagged +
tagged) per VLAN group is unnecessary. Each group now installs a single NAT
entry with an exact VLAN match key.

This also contains a fix for MulticastRouter4 (in P4) using IPv6 ICMP error codes
(ICMP6_DST_UNREACH) instead of IPv4 ones (ICMP_DEST_UNREACH), and removes redundant
entry-count assertions from VLAN lifecycle tests.
@zeeshanlakhani
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@FelixMcFelix updated.

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Test flake in integration_tests::mcast::test_multicast_vlan_translation_not_possible

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