Add --default-mtu. Change default to 65535 (from 9000).

MTU of 9000 was an arbitrary jumbo frame size. Setting the default to the max possible is probably the least likely to cause surprises (especially with patch connections). Add testing of --default-mtu to the test7 example. Co-authored-by: Aaron Brooks <[email protected]>
LonoCloud · Apr 4, 2024 · 714523b · 714523b
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diff --git a/README.md b/README.md
@@ -102,7 +102,7 @@ The following table describes the link properties:
 | dev       | *          | string[15] | eth0    | container intf name      |
 | ip        | *          | CIDR       |         | IP CIDR (index offset)   |
 | mac       | 3          | MAC        |         | MAC addr (index offset)  |
-| mtu       | *          | number 4   | 9000    | intf MTU                 |
+| mtu       | *          | number 4   | 65535   | intf MTU                 |
 | route     | *          | string     |         | ip route add args        |
 | nat       | *          | IP         |         | DNAT/SNAT to IP          |
 | netem     | *          | string     |         | tc qdisc NetEm options   |
@@ -449,8 +449,10 @@ Start the test7 compose configuration:
 docker-compose -f examples/test7-compose.yaml up --build --force-recreate
 ```
 
-Show the links in both node containers to see that the MAC addresses
-are `00:0a:0b:0c:0d:0*` and the MTUs are set to `4111`.
+Show the links in both node containers to see that on the eth0
+interfaces the MAC addresses are `00:0a:0b:0c:0d:0*` and the MTUs are
+set to `4111`. The eth1 interfaces should have the command line set
+default MTU of `5111`.
 
 ```
 docker-compose -f examples/test7-compose.yaml exec --index 1 node ip link

diff --git a/examples/test7-compose.yaml b/examples/test7-compose.yaml
@@ -15,7 +15,7 @@ services:
       - /var/run/docker.sock:/var/run/docker.sock
       - /var/lib/docker:/var/lib/docker
       - ./:/test
-    command: /app/build/conlink.js --compose-file /test/test7-compose.yaml
+    command: /app/build/conlink.js --default-mtu 5111 --compose-file /test/test7-compose.yaml
 
   node:
     image: alpine
@@ -29,3 +29,6 @@ services:
           mac: 00:0a:0b:0c:0d:01
           mtu: 4111
           netem: "delay 40ms rate 10mbit"
+        - bridge: s2
+          ip: 100.0.1.1/16
+          dev: eth1
diff --git a/src/conlink/core.cljs b/src/conlink/core.cljs
@@ -30,6 +30,8 @@ General Options:
   --default-bridge-mode BRIDGE-MODE Default bridge mode (ovs, linux, patch, or auto)
                                     to use for bridge/switch connections
                                     [default: auto] [env: CONLINK_BRIDGE_MODE]
+  --default-mtu MTU                 Default link MTU (for non *vlan types)
+                                    [default: 65535]
   --network-file NETWORK-FILE...    Network config file
   --compose-file COMPOSE-FILE...    Docker compose file with network config
   --compose-project NAME            Docker compose project name for resolving
@@ -100,10 +102,11 @@ General Options:
   Add default values to a link:
     - type: veth
     - dev: eth0
-    - mtu: 9000 (for non *vlan type)
+    - mtu: --default-mtu (for non *vlan type)
     - base: :conlink for veth type, :host for *vlan types, :local otherwise"
   [{:as link :keys [type base bridge ip vlanid]} bridges]
-  (let [type (keyword (or type "veth"))
+  (let [{:keys [default-mtu]} @ctx
+        type (keyword (or type "veth"))
         base-default (cond (= :veth type)     :conlink
                            (VLAN-TYPES type)  :host
                            :else              :local)
@@ -116,7 +119,7 @@ General Options:
                (when bridge
                  {:bridge (get bridges bridge)})
                (when (not (VLAN-TYPES type))
-                 {:mtu  (get link :mtu 9000)}))]
+                 {:mtu  (get link :mtu default-mtu)}))]
     link))
 
 (defn enrich-bridge
@@ -781,6 +784,7 @@ General Options:
      kmod-ovs? (kmod-loaded? "openvswitch")
      kmod-mirred? (kmod-loaded? "act_mirred")
      _ (swap! ctx merge {:default-bridge-mode (:default-bridge-mode opts)
+                         :default-mtu (:default-mtu opts)
                          :kmod-ovs? kmod-ovs?
                          :kmod-mirred? kmod-mirred?})
      network-config (P/-> (load-configs compose-file network-file)