fix(mdns): skip address translation when observed source is IPv6 link… - #6479
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…-local On an IPv6-only LAN, mDNS multicast packets always originate from the sender's link-local address (fe80::/10). _address_translation was replacing the peer's announced routable ULA/global address with this link-local source, making every QUIC dial fail because fe80:: without a zone ID is not routable. Fix: when the observed source is fe80::/10, skip translation entirely and return the announced address unchanged. No NAT is present on a LAN so translation is both unnecessary and harmful here. IPv4 and global IPv6 paths are unaffected. Fixes libp2p#6474
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Hi, and thanks for this!
Can you cargo fmt your changes please?
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cargo fm'ted and introduced the CHANGELOG.md entry
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fix(mdns): skip address translation when observed source is IPv6 link-local
Problem
On an IPv6-only LAN,
extract_discoveredpasses every announced address through_address_translation(address, &observed). Theobservedmultiaddr is built from the mDNS packet's UDP source address, which on an IPv6 LAN is always the sender's link-local address (fe80::/10). This causes the peer's routable ULA address (fd12::1) to be silently replaced with the link-local source, and every subsequent QUIC dial fails becausefe80::without a zone ID is unroutable.The IPv4 path is unaffected because private IPv4 addresses pass through
_address_translationdifferently.Closes #6474.
Fix
Added
observed_is_link_local— a small predicate usingIpv6Addr::is_unicast_link_localfrom std. When it returnstrue,extract_discoveredreturns the announced address as-is and skips_address_translationentirely. No NAT is present on a LAN so translation is both unnecessary and incorrect here.IPv4 and global/ULA IPv6 observed addresses are unaffected.
Tests
test_observed_is_link_local— unit test for the predicate (fe80::,fd12::,192.168.x.x)test_extract_discovered_ipv6_lan_preserves_ula_address— regression: simulates a packet arriving fromfe80::abcd:ef01while the peer announcesfd12::1/udp/4001/quic-v1, asserts the ULA address survives in the output unchangedTesting on real hardware
@ohrensessel has a live IPv6-only ULA setup and has offered to validate this PR against it.