docs(gw): document EdgeOS PPPoE redial procedure

hosts/gw.md

@@ -77,6 +77,30 @@ relevant interface/direction to take effect. Use the operational `show
 firewall` output—not merely the configured rule definitions—to determine the
 effective policy.
 
+## PPPoE redial
+
+To force the `pppoe0` session to reconnect (e.g. to obtain a fresh WAN IP), use
+the operational `disconnect` / `connect` commands — **not** `renew dhcp
+interface`, which applies only to DHCP interfaces:
+
+```bash
+ssh -4 zhiqiang@192.168.66.254
+/opt/vyatta/bin/vyatta-op-cmd-wrapper disconnect interface pppoe0
+/opt/vyatta/bin/vyatta-op-cmd-wrapper connect interface pppoe0
+```
+
+`disconnect` tears down the PPP session; `connect` re-dials immediately. A
+short pause between them (a few seconds, or minutes for cautious ISPs) lets the
+old session finish teardown before redialing. This briefly drops the whole WAN
+uplink and may change the public IPv4 and delegated IPv6 `/60`; in-flight
+sessions and port-forwarded services are interrupted until the new session is
+up.
+
+The `zhiqiang` account logs into `vbash`, not the EdgeOS CLI, so operational
+commands must be invoked through `/opt/vyatta/bin/vyatta-op-cmd-wrapper` and
+depend on its passwordless `sudo`. The `ubnt` account lands directly in the
+operational CLI, where the same commands are entered without the wrapper.
+
 ## Maintenance notes
 
 - EdgeOS writes persistent changes through its configuration tree: enter