envoyproxy/envoy

UDP proxying should track and decrement TTL

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#20,379 opened on Mar 16, 2022

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area/udphelp wanted

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Description

When UDP proxying from A-B it's really unfortunate when bad or misconfigured hardware ends up routing your packets in a loop. Decrementing TTL means you don't end up with that loop being infinite and destroying your CPU.

useful kernel options:

setsockopt(fd, IPPROTO_IP, IP_RECVTTL, &get_ttl, sizeof(get_ttl));

setsockopt(fd, IPPROTO_IPV6, IPV6_RECVHOPLIMIT, &get_ttl, sizeof(get_ttl));

kMinCmsgSpaceForRead += CMSG_SPACE(sizeof(int)) // TTL

if ((cmsg->cmsg_level == IPPROTO_IP && cmsg->cmsg_type == IP_TTL) || (cmsg->cmsg_level == IPPROTO_IPV6 && cmsg->cmsg_type == IPV6_HOPLIMIT)) { ttl = reinterpret_cast<int*>(CMSG_DATA(cmsg)))); }

Contributor guide

Research direction
Inspect the UDP proxy implementation in Envoy, identify where packets are sent and received, and add TTL decrement logic using kernel options IP RECVTTL and IPV6 RECVHOPLIMIT.
Tech stack
cpp
Domain
backend
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
C++Socket programming
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
75