Fix potential blackholing/looping traffic when link-local was used an…

…d refresh ipv6 neighbor to avoid CPU hit (#1904)

* Fix potential blackholing/looping traffic and refresh ipv6 neighbor to avoid CPU hit

In case ipv6 global addresses were configured on L3 interfaces and used for peering,
and routing protocol was using link-local addresses on the same interfaces as prefered nexthops,
the link-local addresses could be aged out after a while due to no activities towards the link-local
addresses themselves. And when we receive new routes with the link-local nexthops, SONiC won't insert
them to the HW, and thus cause looping or blackholing traffic.

Global ipv6 addresses on L3 interfaces between switches are refreshed by BGP keeplive and other messages.

On server facing side, traffic may hit fowarding plane only, and no refresh for the ipv6 neighbor entries regularly.
This could age-out the linux kernel ipv6 neighbor entries, and HW neighbor table entries could be removed,
and thus traffic going to those neighbors would hit CPU, and cause traffic drop and temperary CPU high load.

Also, if link-local addresses were not learned, we may not get them at all later.

It is intended to fix all above issues.

Changes:
Add ndisc6 package in swss docker and use it for ipv6 ndp ping to update the neighbors' state on Vlan interfaces
Change the default ipv6 neighbor reachable timer to 30mins
Add periodical ipv6 multicast ping to ff02::11 to get/refresh link-local neighbor info.

* Fix review comments:
Add PORTCHANNEL_INTERFACE interface for ipv6 multicast ping
format issue

* Combine regular L3 interface and portchannel interface for looping

* Add ndisc6 package to vs docker

build_debian.sh

@@ -303,6 +303,7 @@ set /files/etc/sysctl.conf/net.ipv4.conf.all.arp_notify 1
 set /files/etc/sysctl.conf/net.ipv4.conf.all.arp_ignore 2
 
 set /files/etc/sysctl.conf/net.ipv4.neigh.default.base_reachable_time_ms 1800000
+set /files/etc/sysctl.conf/net.ipv6.neigh.default.base_reachable_time_ms 1800000
 
 set /files/etc/sysctl.conf/net.ipv6.conf.default.forwarding 1
 set /files/etc/sysctl.conf/net.ipv6.conf.all.forwarding 1

dockers/docker-orchagent/Dockerfile.j2

@@ -10,6 +10,7 @@ RUN apt-get update
 
 RUN apt-get install -f -y ifupdown arping libdbus-1-3 libdaemon0 libjansson4
 
+RUN apt-get install -f -y ndisc6
 ## Install redis-tools dependencies
 ## TODO: implicitly install dependencies
 RUN apt-get -y install libjemalloc1

files/scripts/arp_update

@@ -1,10 +1,28 @@
 #!/bin/bash
 #
 # usage:
-# arp_update: Send gratuitous ARP requests to VLAN member neighbors to refresh
-# the neighbors state.
+# arp_update:
+# Send ipv6 multicast pings to all "UP" L3 interfaces including vlan interfaces to
+# refresh link-local addresses from neighbors.
+# Send gratuitous ARP/NDP requests to VLAN member neighbors to refresh
+# the ipv4/ipv6 neighbors state.
 
 while /bin/true; do
+  # find L3 interfaces which are UP, send ipv6 multicast pings
+  echo "{% for (name, prefix) in INTERFACE %} {{name}} {% endfor %}" > /tmp/intf_tmp.j2
+  INTERFACE=`sonic-cfggen -d -t /tmp/intf_tmp.j2`
+  echo "{% for (name, prefix) in PORTCHANNEL_INTERFACE %} {{name}} {% endfor %}" > /tmp/pc_intf_tmp.j2
+  PC_INTERFACE=`sonic-cfggen -d -t /tmp/pc_intf_tmp.j2`
+
+  ALL_INTERFACE="$INTERFACE $PC_INTERFACE"
+  for intf in $ALL_INTERFACE; do
+      ping6cmd="ping6 -I $intf -n -q -i 0 -c 1 -W 0 ff02::1 >/dev/null"
+      intf_up=$(ip link show $intf | grep "state UP")
+      if [[ -n "$intf_up" ]]; then
+          eval $ping6cmd
+      fi
+  done
+
   VLAN=`sonic-cfggen -d -v 'VLAN.keys() | join(" ") if VLAN'`
   for vlan in $VLAN; do
       # generate a list of arping commands:
@@ -15,6 +33,18 @@ while /bin/true; do
       ipcmd="ip -4 neigh show | grep $vlan | cut -d ' ' -f 1,3 | $arpingcmd"
 
       eval `eval $ipcmd`
+
+      # send ipv6 multicast pings to Vlan interfaces to get/refresh link-local addrs
+      ping6cmd="ping6 -I $vlan -n -q -i 0 -c 1 -W 0 ff02::1 >/dev/null"
+      eval $ping6cmd
+
+      # generate a list of ndisc6 commands (exclude link-local addrs since it is done above):
+      #   ndisc6 -q -w 0 -1 <IP 1> <VLAN interface>;
+      #   ndisc6 -q -w 0 -1 <IP 2> <VLAN interface>;
+      #   ...
+      ndisc6cmd="sed -e 's/^/ndisc6 -q -w 0 -1 /' -e 's/$/;/'"
+      ip6cmd="ip -6 neigh show | grep -v fe80 | grep $vlan | cut -d ' ' -f 1,3 | $ndisc6cmd"
+      eval `eval $ip6cmd`
   done
   sleep 300
 done

platform/vs/docker-sonic-vs/Dockerfile.j2

@@ -13,6 +13,7 @@ RUN apt-get update
 
 RUN apt-get install -y net-tools \
                        arping \
+                       ndisc6 \
                        ethtool \
                        tcpdump \
                        ifupdown \