networkd-ndisc: handle missing mtu gracefully (#4913)

At least bird's implementation of router advertisement does not
set MTU option by default (instead it supplies an option to the user).
In this case just leave MTU as it is.

diff --git a/src/network/networkd-ndisc.c b/src/network/networkd-ndisc.c
index 5320592f7a22d4a82a1773842b42de5520cff1bb..5097ab9d7204453201927c8ecb5518ccaa5d4e1f 100644 (file)
--- a/src/network/networkd-ndisc.c
+++ b/src/network/networkd-ndisc.c
@@ -118,7 +118,9 @@ static void ndisc_router_process_default(Link *link, sd_ndisc_router *rt) {
         }
 
         r = sd_ndisc_router_get_mtu(rt, &mtu);
-        if (r < 0) {
+        if (r == -ENODATA)
+                mtu = 0;
+        else if (r < 0) {
                 log_link_warning_errno(link, r, "Failed to get default router MTU from RA: %m");
                 return;
         }