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<p class="MsoNormal">The <span style="font-family:"Courier New"">RetransmitSec</span> option was introduced in
<b>systemd-v255</b>, but I cannot get it to work for Neighbor Solicitations from a Host. Instead, I observe that the NS are always transmitted at 1 second intervals, regardless of whether it was changed by:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<ol style="margin-top:0cm" start="1" type="1">
<li class="MsoListParagraph" style="margin-left:18.0pt;mso-list:l2 level1 lfo4">Received RA Retransmit Timer<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:18.0pt;mso-list:l2 level1 lfo4">Sysctl net.ipv6.icmp.ratelimit<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:18.0pt;mso-list:l2 level1 lfo4">Systemd.network configuration file RetransmitSec<o:p></o:p></li></ol>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">A few questions:<o:p></o:p></p>
<ol style="margin-top:0cm" start="1" type="1">
<li class="MsoListParagraph" style="margin-left:18.0pt;mso-list:l4 level1 lfo5">Can you point me at the networkd code that generates the neighbor solicitations?<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:18.0pt;mso-list:l4 level1 lfo5">My router sends an RA with a Retransmit Timer = 5000ms:<o:p></o:p></li><ol style="margin-top:0cm" start="1" type="a">
<li class="MsoListParagraph" style="margin-left:0cm;mso-list:l4 level2 lfo5">What is supposed to take precedence, the RA or the value in the config file?<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0cm;mso-list:l4 level2 lfo5">With debug enabled, I see networkd writes to
<span style="font-size:10.5pt;font-family:Consolas;color:#4472C4;mso-ligatures:none;mso-fareast-language:EN-GB">
/proc/sys/net/ipv6/icmp/ratelimit</span><span style="color:#4472C4"> </span><o:p></o:p></li></ol>
</ol>
<p class="MsoListParagraph" style="margin-left:108.0pt;text-indent:-108.0pt;mso-text-indent-alt:-9.0pt;mso-list:l4 level3 lfo5">
<![if !supportLists]><span style="mso-list:Ignore"><span style="font:7.0pt "Times New Roman"">
</span>i.<span style="font:7.0pt "Times New Roman""> </span></span><![endif]>However, that makes no difference to the retransmit rate, which is always 1 second.<o:p></o:p></p>
<ol style="margin-top:0cm" start="3" type="1">
<li class="MsoListParagraph" style="margin-left:18.0pt;mso-list:l4 level1 lfo5">Why is this option not enabled under [Network], but instead under [IPv6SendRA]. Hosts send NS that should also be ratelimited.<o:p></o:p></li></ol>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">$ systemctl --version<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">systemd 255 (255-1-g6a9a58c^)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">+PAM -AUDIT -SELINUX -APPARMOR -IMA -SMACK -SECCOMP -GCRYPT -GNUTLS -OPENSSL -ACL +BLKID -CURL -ELFUTILS -FIDO2 -IDN2 -IDN -IPTC +KMOD -LIBCRYPTSETUP +LIBFDISK -PCRE2 -PWQUALITY -P11KIT
-QRENCODE -TPM2 -BZIP2 -LZ4 +XZ -ZLIB -ZSTD -BPF_FRAMEWORK -XKBCOMMON -UTMP +SYSVINIT default-hierarchy=hybrid<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’ve tried several configuration changes, but nothing worked. E.g. I tried to configure the Retransmit interval to 3 seconds. After each configuration change, I ran:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">$ systemctl daemon-reload; systemctl restart systemd-networkd<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">One of my attempts:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">$ networkctl cat 10-eno0.network<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""># /etc/systemd/network/10-eno0.network<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">[Match]<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">KernelCommandLine=!nfsroot<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">Name=eno0<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">[DHCP]<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">ClientIdentifier=mac<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">RouteMetric=10<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">UseDomains=yes<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">UseHostname=yes<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">UseMTU=yes<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">[IPv6AcceptRA]<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">#UseOnLinkPrefix=yes<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">UseDNS=yes<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">UseDomains=yes<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">[Link]<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">RequiredForOnline=no<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">[Network]<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">#Address=16.107.234.71/21<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">#DHCP=ipv6<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">#DNS=1.2.3.6<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">#Gateway=16.107.232.1<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">Address=10.1.1.1/24<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">DHCP=no<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">Gateway=10.1.1.2<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">IPv6AcceptRA=yes<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">IPv6SendRA=yes<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">[IPv6SendRA]<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">RetransmitSec=3<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">And here is the tcpdump output:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">$ tcpdump -i eno0 -n --number ip6 -vv<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">tcpdump: listening on eno0, link-type EN10MB (Ethernet), snapshot length 262144 bytes<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""> 1 02:23:50.607129 IP6 (hlim 255, next-header ICMPv6 (58) payload length: 56) fe80::200:10ff:fe10:1060 > ff02::1: [icmp6 sum ok] ICMP6, router advertisement, length 56<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""> hop limit 64, Flags [none], pref medium, router lifetime 9000s, reachable time 30000ms,
<span style="background:yellow;mso-highlight:yellow">retrans timer 5000ms</span><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""> prefix info option (3), length 32 (4): 2001:2:0:1000::/64, Flags [onlink, auto], valid time 65535s, pref. time 65535s<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""> 0x0000: 40c0 0000 ffff 0000 ffff 0000 0000 2001<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""> 0x0010: 0002 0000 1000 0000 0000 0000 0000<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""> mtu option (5), length 8 (1): 1500<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""> 0x0000: 0000 0000 05dc<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""> 8< -- snip unrelated multicast packets ---- >8<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""> 4 02:24:00.932029 IP6 (hlim 255, next-header ICMPv6 (58) payload length: 10) fe80::200:10ff:fe10:1081 > fe80::9640:c9ff:fed6:77f6: [icmp6 sum ok] ICMP6, echo request, id 0, seq
0<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""> 5
<span style="background:yellow;mso-highlight:yellow">02:24:00</span>.932412 IP6 (hlim 255, next-header ICMPv6 (58) payload length: 32) fe80::9640:c9ff:fed6:77f6 > ff02::1:ff10:1081: [icmp6 sum ok] ICMP6,
<span style="background:yellow;mso-highlight:yellow">neighbor solicitation</span>, length 32, who has fe80::200:10ff:fe10:1081<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""> source link-address option (1), length 8 (1): 94:40:c9:d6:77:f6<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""> 0x0000: 9440 c9d6 77f6<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""> 6
<span style="background:yellow;mso-highlight:yellow">02:24:01</span>.934639 IP6 (hlim 255, next-header ICMPv6 (58) payload length: 32) fe80::9640:c9ff:fed6:77f6 > ff02::1:ff10:1081: [icmp6 sum ok] ICMP6,
<span style="background:yellow;mso-highlight:yellow">neighbor solicitation</span>, length 32, who has fe80::200:10ff:fe10:1081<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""> source link-address option (1), length 8 (1): 94:40:c9:d6:77:f6<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""> 0x0000: 9440 c9d6 77f6<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""> 7
<span style="background:yellow;mso-highlight:yellow">02:24:02</span>.958599 IP6 (hlim 255, next-header ICMPv6 (58) payload length: 32) fe80::9640:c9ff:fed6:77f6 > ff02::1:ff10:1081: [icmp6 sum ok] ICMP6,
<span style="background:yellow;mso-highlight:yellow">neighbor solicitation</span>, length 32, who has fe80::200:10ff:fe10:1081<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""> source link-address option (1), length 8 (1): 94:40:c9:d6:77:f6<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""> 0x0000: 9440 c9d6 77f6<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">$ sysctl net.ipv6.icmp.ratelimit<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">net.ipv6.icmp.ratelimit = 5000<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks,<o:p></o:p></p>
<p class="MsoNormal">Matt.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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