[PATCH v2 20/23] test: Reconfigure IPv6 address after changing MTU

[David Gibson <david@gibson.dropbear.id.au>]

In the TCP throughput tests, we adjust the guest's MTU in order to test
various packet sizes.  Some of those are below 1280 which causes IPv6 to
be deconfigured on the guest interface.  When we increase it above 1280
again, IPv6 is re-enabled and we get an address in the right prefix with
NDP, but we don't get exactly the expected address back - that's only
communicated with --config-net or DHCPv6.

With changes to how we handle NAT this can cause some of the IPv6 tests to
fail, because they don't use the address that passt/pasta expects, and the
guest doesn't initiate any traffic which allows us to learn what the new
address is.

Work around this by re-invoking dhclient -6 between adjusting the MTU and
running IPv6 test cases.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 test/perf/passt_tcp | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/test/perf/passt_tcp b/test/perf/passt_tcp
index 695479f3..635998e1 100644
--- a/test/perf/passt_tcp
+++ b/test/perf/passt_tcp
@@ -112,6 +112,10 @@ bw	__BW__ 7.0 8.0
 
 iperf3k	ns
 
+# Reducing MTU below 1280 deconfigures IPv6, get our address back
+guest	dhclient -6 -x
+guest	dhclient -6 __IFNAME__
+
 tl	TCP RR latency over IPv4: guest to host
 lat	-
 lat	-
-- 
@@ -112,6 +112,10 @@ bw	__BW__ 7.0 8.0
 
 iperf3k	ns
 
+# Reducing MTU below 1280 deconfigures IPv6, get our address back
+guest	dhclient -6 -x
+guest	dhclient -6 __IFNAME__
+
 tl	TCP RR latency over IPv4: guest to host
 lat	-
 lat	-
-- 
2.46.0