From patchwork Tue Jul 20 20:35:29 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Vadim Fedorenko X-Patchwork-Id: 481979 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 743ECC07E95 for ; Tue, 20 Jul 2021 20:50:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 54F6C61019 for ; Tue, 20 Jul 2021 20:50:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237059AbhGTUJ0 (ORCPT ); Tue, 20 Jul 2021 16:09:26 -0400 Received: from novek.ru ([213.148.174.62]:46650 "EHLO novek.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237733AbhGTTzI (ORCPT ); Tue, 20 Jul 2021 15:55:08 -0400 Received: from nat1.ooonet.ru (gw.zelenaya.net [91.207.137.40]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by novek.ru (Postfix) with ESMTPSA id 5C37F503E25; Tue, 20 Jul 2021 23:33:18 +0300 (MSK) DKIM-Filter: OpenDKIM Filter v2.11.0 novek.ru 5C37F503E25 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=novek.ru; s=mail; t=1626813200; bh=GW4Vmih5xj74VjcgQGvWz7Y5V5BTKkO8qSbc9G03p/A=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Dy1PSN8B3Ir6bIvvY6F1MdpInE0T+DSkEIj8Yquaq94cTLIDRDRwHwgwLrx1lC9MF 03II+M2MeC57psQx62IEYdHgKfur4AGzWAC6Ng2B56zl5kuiAXlwYhucfdTfjMMp57 iC60eLyyFWPbfbvBZe/lWVRZpJ+fUC7aRKUoKYU0= From: Vadim Fedorenko To: David Ahern , Willem de Bruijn , Paolo Abeni , Xin Long Cc: Jakub Kicinski , "David S. Miller" , netdev@vger.kernel.org, Vadim Fedorenko Subject: [PATCH net v3 2/2] selftests: net: add ESP-in-UDP PMTU test Date: Tue, 20 Jul 2021 23:35:29 +0300 Message-Id: <20210720203529.21601-3-vfedorenko@novek.ru> X-Mailer: git-send-email 2.18.4 In-Reply-To: <20210720203529.21601-1-vfedorenko@novek.ru> References: <20210720203529.21601-1-vfedorenko@novek.ru> Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org The case of ESP in UDP encapsulation was not covered before. Add cases of local changes of MTU and difference on routed path. Signed-off-by: Vadim Fedorenko --- tools/testing/selftests/net/nettest.c | 55 ++++++- tools/testing/selftests/net/pmtu.sh | 212 +++++++++++++++++++++++++- 2 files changed, 260 insertions(+), 7 deletions(-) diff --git a/tools/testing/selftests/net/nettest.c b/tools/testing/selftests/net/nettest.c index 6365c7fd1262..bd6288302094 100644 --- a/tools/testing/selftests/net/nettest.c +++ b/tools/testing/selftests/net/nettest.c @@ -11,9 +11,11 @@ #include #include #include +#include #include #include #include +#include #include #include #include @@ -27,6 +29,10 @@ #include #include +#include +#include +#include + #ifndef IPV6_UNICAST_IF #define IPV6_UNICAST_IF 76 #endif @@ -114,6 +120,9 @@ struct sock_args { struct in_addr in; struct in6_addr in6; } expected_raddr; + + /* ESP in UDP encap test */ + int use_xfrm; }; static int server_mode; @@ -1346,6 +1355,41 @@ static int bind_socket(int sd, struct sock_args *args) return 0; } +static int config_xfrm_policy(int sd, struct sock_args *args) +{ + struct xfrm_userpolicy_info policy = {}; + int type = UDP_ENCAP_ESPINUDP; + int xfrm_af = IP_XFRM_POLICY; + int level = SOL_IP; + + if (args->type != SOCK_DGRAM) { + log_error("Invalid socket type. Only DGRAM could be used for XFRM\n"); + return 1; + } + + policy.action = XFRM_POLICY_ALLOW; + policy.sel.family = args->version; + if (args->version == AF_INET6) { + xfrm_af = IPV6_XFRM_POLICY; + level = SOL_IPV6; + } + + policy.dir = XFRM_POLICY_OUT; + if (setsockopt(sd, level, xfrm_af, &policy, sizeof(policy)) < 0) + return 1; + + policy.dir = XFRM_POLICY_IN; + if (setsockopt(sd, level, xfrm_af, &policy, sizeof(policy)) < 0) + return 1; + + if (setsockopt(sd, IPPROTO_UDP, UDP_ENCAP, &type, sizeof(type)) < 0) { + log_err_errno("Failed to set xfrm encap"); + return 1; + } + + return 0; +} + static int lsock_init(struct sock_args *args) { long flags; @@ -1389,6 +1433,11 @@ static int lsock_init(struct sock_args *args) if (fcntl(sd, F_SETFD, FD_CLOEXEC) < 0) log_err_errno("Failed to set close-on-exec flag"); + if (args->use_xfrm && config_xfrm_policy(sd, args)) { + log_err_errno("Failed to set xfrm policy"); + goto err; + } + out: return sd; @@ -1772,7 +1821,7 @@ static int ipc_parent(int cpid, int fd, struct sock_args *args) return client_status; } -#define GETOPT_STR "sr:l:c:p:t:g:P:DRn:M:X:m:d:I:BN:O:SCi6L:0:1:2:3:Fbq" +#define GETOPT_STR "sr:l:c:p:t:g:P:DRn:M:X:m:d:I:BN:O:SCi6xL:0:1:2:3:Fbq" static void print_usage(char *prog) { @@ -1795,6 +1844,7 @@ static void print_usage(char *prog) " -D|R datagram (D) / raw (R) socket (default stream)\n" " -l addr local address to bind to in server mode\n" " -c addr local address to bind to in client mode\n" + " -x configure XFRM policy on socket\n" "\n" " -d dev bind socket to given device name\n" " -I dev bind socket to given device name - server mode\n" @@ -1966,6 +2016,9 @@ int main(int argc, char *argv[]) case 'q': quiet = 1; break; + case 'x': + args.use_xfrm = 1; + break; default: print_usage(argv[0]); return 1; diff --git a/tools/testing/selftests/net/pmtu.sh b/tools/testing/selftests/net/pmtu.sh index 64cd2e23c568..ac67bd78081a 100755 --- a/tools/testing/selftests/net/pmtu.sh +++ b/tools/testing/selftests/net/pmtu.sh @@ -118,6 +118,16 @@ # below for IPv6 doesn't apply here, because, on IPv4, administrative MTU # changes alone won't affect PMTU # +# - pmtu_vti4_udp_exception +# Same as pmtu_vti4_exception, but using ESP-in-UDP +# +# - pmtu_vti4_udp_routed_exception +# Set up vti tunnel on top of veth connected through routing namespace and +# add xfrm states and policies with ESP-in-UDP encapsulation. Check that +# route exception is not created if link layer MTU is not exceeded, then +# lower MTU on second part of routed environment and check that exception +# is created with the expected PMTU. +# # - pmtu_vti6_exception # Set up vti6 tunnel on top of veth, with xfrm states and policies, in two # namespaces with matching endpoints. Check that route exception is @@ -125,6 +135,13 @@ # decrease and increase MTU of tunnel, checking that route exception PMTU # changes accordingly # +# - pmtu_vti6_udp_exception +# Same as pmtu_vti6_exception, but using ESP-in-UDP +# +# - pmtu_vti6_udp_routed_exception +# Same as pmtu_vti6_udp_routed_exception but with routing between vti +# endpoints +# # - pmtu_vti4_default_mtu # Set up vti4 tunnel on top of veth, in two namespaces with matching # endpoints. Check that MTU assigned to vti interface is the MTU of the @@ -224,6 +241,10 @@ tests=" pmtu_ipv6_ipv6_exception IPv6 over IPv6: PMTU exceptions 1 pmtu_vti6_exception vti6: PMTU exceptions 0 pmtu_vti4_exception vti4: PMTU exceptions 0 + pmtu_vti6_udp_exception vti6: PMTU exceptions (ESP-in-UDP) 0 + pmtu_vti4_udp_exception vti4: PMTU exceptions (ESP-in-UDP) 0 + pmtu_vti6_udp_routed_exception vti6: PMTU exceptions, routed (ESP-in-UDP) 0 + pmtu_vti4_udp_routed_exception vti4: PMTU exceptions, routed (ESP-in-UDP) 0 pmtu_vti4_default_mtu vti4: default MTU assignment 0 pmtu_vti6_default_mtu vti6: default MTU assignment 0 pmtu_vti4_link_add_mtu vti4: MTU setting on link creation 0 @@ -246,7 +267,6 @@ ns_b="ip netns exec ${NS_B}" ns_c="ip netns exec ${NS_C}" ns_r1="ip netns exec ${NS_R1}" ns_r2="ip netns exec ${NS_R2}" - # Addressing and routing for tests with routers: four network segments, with # index SEGMENT between 1 and 4, a common prefix (PREFIX4 or PREFIX6) and an # identifier ID, which is 1 for hosts (A and B), 2 for routers (R1 and R2). @@ -279,7 +299,6 @@ routes=" A ${prefix6}:${b_r2}::1 ${prefix6}:${a_r2}::2 B default ${prefix6}:${b_r1}::2 " - USE_NH="no" # ns family nh id destination gateway nexthops=" @@ -326,6 +345,7 @@ dummy6_mask="64" err_buf= tcpdump_pids= +nettest_pids= err() { err_buf="${err_buf}${1} @@ -548,6 +568,14 @@ setup_vti6() { setup_vti 6 ${veth6_a_addr} ${veth6_b_addr} ${tunnel6_a_addr} ${tunnel6_b_addr} ${tunnel6_mask} } +setup_vti4routed() { + setup_vti 4 ${prefix4}.${a_r1}.1 ${prefix4}.${b_r1}.1 ${tunnel4_a_addr} ${tunnel4_b_addr} ${tunnel4_mask} +} + +setup_vti6routed() { + setup_vti 6 ${prefix6}:${a_r1}::1 ${prefix6}:${b_r1}::1 ${tunnel6_a_addr} ${tunnel6_b_addr} ${tunnel6_mask} +} + setup_vxlan_or_geneve() { type="${1}" a_addr="${2}" @@ -619,18 +647,36 @@ setup_xfrm() { proto=${1} veth_a_addr="${2}" veth_b_addr="${3}" + encap=${4} - run_cmd ${ns_a} ip -${proto} xfrm state add src ${veth_a_addr} dst ${veth_b_addr} spi 0x1000 proto esp aead 'rfc4106(gcm(aes))' 0x0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f 128 mode tunnel || return 1 - run_cmd ${ns_a} ip -${proto} xfrm state add src ${veth_b_addr} dst ${veth_a_addr} spi 0x1001 proto esp aead 'rfc4106(gcm(aes))' 0x0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f 128 mode tunnel + run_cmd ${ns_a} ip -${proto} xfrm state add src ${veth_a_addr} dst ${veth_b_addr} spi 0x1000 proto esp aead 'rfc4106(gcm(aes))' 0x0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f 128 mode tunnel ${encap} || return 1 + run_cmd ${ns_a} ip -${proto} xfrm state add src ${veth_b_addr} dst ${veth_a_addr} spi 0x1001 proto esp aead 'rfc4106(gcm(aes))' 0x0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f 128 mode tunnel ${encap} run_cmd ${ns_a} ip -${proto} xfrm policy add dir out mark 10 tmpl src ${veth_a_addr} dst ${veth_b_addr} proto esp mode tunnel run_cmd ${ns_a} ip -${proto} xfrm policy add dir in mark 10 tmpl src ${veth_b_addr} dst ${veth_a_addr} proto esp mode tunnel - run_cmd ${ns_b} ip -${proto} xfrm state add src ${veth_a_addr} dst ${veth_b_addr} spi 0x1000 proto esp aead 'rfc4106(gcm(aes))' 0x0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f 128 mode tunnel - run_cmd ${ns_b} ip -${proto} xfrm state add src ${veth_b_addr} dst ${veth_a_addr} spi 0x1001 proto esp aead 'rfc4106(gcm(aes))' 0x0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f 128 mode tunnel + run_cmd ${ns_b} ip -${proto} xfrm state add src ${veth_a_addr} dst ${veth_b_addr} spi 0x1000 proto esp aead 'rfc4106(gcm(aes))' 0x0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f 128 mode tunnel ${encap} + run_cmd ${ns_b} ip -${proto} xfrm state add src ${veth_b_addr} dst ${veth_a_addr} spi 0x1001 proto esp aead 'rfc4106(gcm(aes))' 0x0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f0f 128 mode tunnel ${encap} run_cmd ${ns_b} ip -${proto} xfrm policy add dir out mark 10 tmpl src ${veth_b_addr} dst ${veth_a_addr} proto esp mode tunnel run_cmd ${ns_b} ip -${proto} xfrm policy add dir in mark 10 tmpl src ${veth_a_addr} dst ${veth_b_addr} proto esp mode tunnel } +setup_nettest_xfrm() { + which nettest >/dev/null + if [ $? -ne 0 ]; then + echo "'nettest' command not found; skipping tests" + return 1 + fi + + [ ${1} -eq 6 ] && proto="-6" || proto="" + port=${2} + + run_cmd ${ns_a} nettest ${proto} -q -D -s -x -p ${port} -t 5 & + nettest_pids="${nettest_pids} $!" + + run_cmd ${ns_b} nettest ${proto} -q -D -s -x -p ${port} -t 5 & + nettest_pids="${nettest_pids} $!" +} + setup_xfrm4() { setup_xfrm 4 ${veth4_a_addr} ${veth4_b_addr} } @@ -639,6 +685,26 @@ setup_xfrm6() { setup_xfrm 6 ${veth6_a_addr} ${veth6_b_addr} } +setup_xfrm4udp() { + setup_xfrm 4 ${veth4_a_addr} ${veth4_b_addr} "encap espinudp 4500 4500 0.0.0.0" + setup_nettest_xfrm 4 4500 +} + +setup_xfrm6udp() { + setup_xfrm 6 ${veth6_a_addr} ${veth6_b_addr} "encap espinudp 4500 4500 0.0.0.0" + setup_nettest_xfrm 6 4500 +} + +setup_xfrm4udprouted() { + setup_xfrm 4 ${prefix4}.${a_r1}.1 ${prefix4}.${b_r1}.1 "encap espinudp 4500 4500 0.0.0.0" + setup_nettest_xfrm 4 4500 +} + +setup_xfrm6udprouted() { + setup_xfrm 6 ${prefix6}:${a_r1}::1 ${prefix6}:${b_r1}::1 "encap espinudp 4500 4500 0.0.0.0" + setup_nettest_xfrm 6 4500 +} + setup_routing_old() { for i in ${routes}; do [ "${ns}" = "" ] && ns="${i}" && continue @@ -823,6 +889,11 @@ cleanup() { done tcpdump_pids= + for pid in ${nettest_pids}; do + kill ${pid} + done + nettest_pids= + for n in ${NS_A} ${NS_B} ${NS_C} ${NS_R1} ${NS_R2}; do ip netns del ${n} 2> /dev/null done @@ -1432,6 +1503,135 @@ test_pmtu_vti6_exception() { return ${fail} } +test_pmtu_vti4_udp_exception() { + setup namespaces veth vti4 xfrm4udp || return $ksft_skip + trace "${ns_a}" veth_a "${ns_b}" veth_b \ + "${ns_a}" vti4_a "${ns_b}" vti4_b + + veth_mtu=1500 + vti_mtu=$((veth_mtu - 20)) + + # UDP SPI SN IV ICV pad length next header + esp_payload_rfc4106=$((vti_mtu - 8 - 4 - 4 - 8 - 16 - 1 - 1)) + ping_payload=$((esp_payload_rfc4106 - 28)) + + mtu "${ns_a}" veth_a ${veth_mtu} + mtu "${ns_b}" veth_b ${veth_mtu} + mtu "${ns_a}" vti4_a ${vti_mtu} + mtu "${ns_b}" vti4_b ${vti_mtu} + + # Send DF packet without exceeding link layer MTU, check that no + # exception is created + run_cmd ${ns_a} ping -q -M want -i 0.1 -w 1 -s ${ping_payload} ${tunnel4_b_addr} + pmtu="$(route_get_dst_pmtu_from_exception "${ns_a}" ${tunnel4_b_addr})" + check_pmtu_value "" "${pmtu}" "sending packet smaller than PMTU (IP payload length ${esp_payload_rfc4106})" || return 1 + + # Now exceed link layer MTU by one byte, check that exception is created + # with the right PMTU value + run_cmd ${ns_a} ping -q -M want -i 0.1 -w 1 -s $((ping_payload + 1)) ${tunnel4_b_addr} + pmtu="$(route_get_dst_pmtu_from_exception "${ns_a}" ${tunnel4_b_addr})" + check_pmtu_value "${esp_payload_rfc4106}" "${pmtu}" "exceeding PMTU (IP payload length $((esp_payload_rfc4106 + 1)))" +} + +test_pmtu_vti6_udp_exception() { + setup namespaces veth vti6 xfrm6udp || return $ksft_skip + trace "${ns_a}" veth_a "${ns_b}" veth_b \ + "${ns_a}" vti6_a "${ns_b}" vti6_b + fail=0 + + # Create route exception by exceeding link layer MTU + mtu "${ns_a}" veth_a 4000 + mtu "${ns_b}" veth_b 4000 + mtu "${ns_a}" vti6_a 5000 + mtu "${ns_b}" vti6_b 5000 + run_cmd ${ns_a} ${ping6} -q -i 0.1 -w 1 -s 60000 ${tunnel6_b_addr} + + # Check that exception was created + pmtu="$(route_get_dst_pmtu_from_exception "${ns_a}" ${tunnel6_b_addr})" + check_pmtu_value any "${pmtu}" "creating tunnel exceeding link layer MTU" || return 1 + + # Decrease tunnel MTU, check for PMTU decrease in route exception + mtu "${ns_a}" vti6_a 3000 + pmtu="$(route_get_dst_pmtu_from_exception "${ns_a}" ${tunnel6_b_addr})" + check_pmtu_value "3000" "${pmtu}" "decreasing tunnel MTU" || fail=1 + + # Increase tunnel MTU, check for PMTU increase in route exception + mtu "${ns_a}" vti6_a 9000 + pmtu="$(route_get_dst_pmtu_from_exception "${ns_a}" ${tunnel6_b_addr})" + check_pmtu_value "9000" "${pmtu}" "increasing tunnel MTU" || fail=1 + + return ${fail} +} + +test_pmtu_vti4_udp_routed_exception() { + setup namespaces routing vti4routed xfrm4udprouted || return $ksft_skip + trace "${ns_a}" veth_A-R1 "${ns_b}" veth_B-R1 \ + "${ns_a}" vti4_a "${ns_b}" vti4_b + + veth_mtu=1500 + vti_mtu=$((veth_mtu - 20)) + + # UDP SPI SN IV ICV pad length next header + esp_payload_rfc4106=$((vti_mtu - 8 - 4 - 4 - 8 - 16 - 1 - 1)) + ping_payload=$((esp_payload_rfc4106 - 28)) + + mtu "${ns_a}" veth_A-R1 ${veth_mtu} + mtu "${ns_r1}" veth_R1-A ${veth_mtu} + mtu "${ns_b}" veth_B-R1 ${veth_mtu} + mtu "${ns_r1}" veth_R1-B ${veth_mtu} + + mtu "${ns_a}" vti4_a ${vti_mtu} + mtu "${ns_b}" vti4_b ${vti_mtu} + + # Send DF packet without exceeding link layer MTU, check that no + # exception is created + run_cmd ${ns_a} ping -q -M want -i 0.1 -w 1 -s ${ping_payload} ${tunnel4_b_addr} + pmtu="$(route_get_dst_pmtu_from_exception "${ns_a}" ${tunnel4_b_addr})" + check_pmtu_value "" "${pmtu}" "sending packet smaller than PMTU (IP payload length ${esp_payload_rfc4106})" || return 1 + + # Now decrease link layer MTU by 8 bytes on R1, check that exception is created + # with the right PMTU value + mtu "${ns_r1}" veth_R1-B $((veth_mtu - 8)) + run_cmd ${ns_a} ping -q -M want -i 0.1 -w 1 -s $((ping_payload)) ${tunnel4_b_addr} + pmtu="$(route_get_dst_pmtu_from_exception "${ns_a}" ${tunnel4_b_addr})" + check_pmtu_value "$((esp_payload_rfc4106 - 8))" "${pmtu}" "exceeding PMTU (IP payload length $((esp_payload_rfc4106)))" +} + +test_pmtu_vti6_udp_routed_exception() { + setup namespaces routing vti6routed xfrm6udprouted || return $ksft_skip + trace "${ns_a}" veth_A-R1 "${ns_b}" veth_B-R1 \ + "${ns_a}" vti6_a "${ns_b}" vti6_b + + veth_mtu=1500 + vti_mtu=$((veth_mtu - 40)) + + # UDP SPI SN IV ICV pad length next header + esp_payload_rfc4106=$((vti_mtu - 8 - 4 - 4 - 8 - 16 - 1 - 1)) + ping_payload=$((esp_payload_rfc4106 - 48)) + + mtu "${ns_a}" veth_A-R1 ${veth_mtu} + mtu "${ns_r1}" veth_R1-A ${veth_mtu} + mtu "${ns_b}" veth_B-R1 ${veth_mtu} + mtu "${ns_r1}" veth_R1-B ${veth_mtu} + + # mtu "${ns_a}" vti6_a ${vti_mtu} + # mtu "${ns_b}" vti6_b ${vti_mtu} + + run_cmd ${ns_a} ${ping6} -q -M want -i 0.1 -w 1 -s ${ping_payload} ${tunnel6_b_addr} + + # Check that exception was not created + pmtu="$(route_get_dst_pmtu_from_exception "${ns_a}" ${tunnel6_b_addr})" + check_pmtu_value "" "${pmtu}" "sending packet smaller than PMTU (IP payload length ${esp_payload_rfc4106})" || return 1 + + # Now decrease link layer MTU by 8 bytes on R1, check that exception is created + # with the right PMTU value + mtu "${ns_r1}" veth_R1-B $((veth_mtu - 8)) + run_cmd ${ns_a} ${ping6} -q -M want -i 0.1 -w 1 -s $((ping_payload)) ${tunnel6_b_addr} + pmtu="$(route_get_dst_pmtu_from_exception "${ns_a}" ${tunnel6_b_addr})" + check_pmtu_value "$((esp_payload_rfc4106 - 8))" "${pmtu}" "exceeding PMTU (IP payload length $((esp_payload_rfc4106)))" + +} + test_pmtu_vti4_default_mtu() { setup namespaces veth vti4 || return $ksft_skip