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selftests: traceroute: Test traceroute with different source IPs

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When generating ICMP error messages, the kernel will prefer a source IP
that is on the same subnet as the destination IP (see
inet_select_addr()). Test this behavior by invoking traceroute with
different source IPs and checking that the ICMP error message is
generated with a source IP in the same subnet.

Reviewed-by: Petr Machata <petrm@nvidia.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Link: https://patch.msgid.link/20250908073238.119240-8-idosch@nvidia.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Ido Schimmel 2025-09-08 10:32:37 +03:00 committed by Paolo Abeni
parent 5c9c78224f
commit 2e6428100b
1 changed files with 9 additions and 4 deletions
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13
tools/testing/selftests/net/traceroute.sh
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@ -196,9 +196,10 @@ run_traceroute6()
################################################################################
# traceroute test
#
# Verify that traceroute from H1 to H2 shows 1.0.1.1 in this scenario
# Verify that traceroute from H1 to H2 shows 1.0.3.1 and 1.0.1.1 when
# traceroute uses 1.0.3.3 and 1.0.1.3 as the source IP, respectively.
#
# 1.0.3.1/24
# 1.0.3.3/24 1.0.3.1/24
# ---- 1.0.1.3/24 1.0.1.1/24 ---- 1.0.2.1/24 1.0.2.4/24 ----
# |H1|--------------------------|R1|--------------------------|H2|
# ---- N1 ---- N2 ----
@ -226,6 +227,7 @@ setup_traceroute()
connect_ns $h1 eth0 1.0.1.3/24 - \
$router eth1 1.0.3.1/24 -
ip -n "$h1" addr add 1.0.3.3/24 dev eth0
ip netns exec $h1 ip route add default via 1.0.1.1
ip netns exec $router ip addr add 1.0.1.1/24 dev eth1
@ -248,9 +250,12 @@ run_traceroute()
RET=0
# traceroute host-2 from host-1 (expects 1.0.1.1). Takes a while.
run_cmd $h1 "traceroute 1.0.2.4 | grep -q 1.0.1.1"
# traceroute host-2 from host-1. Expect a source IP that is on the same
# subnet as destination IP of the ICMP error message.
run_cmd "$h1" "traceroute -s 1.0.1.3 1.0.2.4 | grep -q 1.0.1.1"
check_err $? "traceroute did not return 1.0.1.1"
run_cmd "$h1" "traceroute -s 1.0.3.3 1.0.2.4 | grep -q 1.0.3.1"
check_err $? "traceroute did not return 1.0.3.1"
log_test "IPv4 traceroute"
cleanup_traceroute