Set value of SCOPE to SCOPE_LINK for opt121 routes with router unspecified with DHCP

    Default behavior of the plugin is to try and install routes without
    specifying SCOPE which results in not installing certain routes that
    do not have a gateway set in the DHCP server response. If the SCOPE is
    not set to LINK (in particuliar for NICs in some cloud environment
    that get assigned /32 IPs to them). This change enables routes to be
    installed without the router being specified, but sets to SCOPE_LINK.

Signed-off-by: Olivier <martinolivier@google.com>

Author: omartin2010

plugins/ipam/dhcp/lease.go

@@ -474,11 +474,13 @@ func (l *DHCPLease) Routes() []*types.Route {
 	opt121Routes := ack.ClasslessStaticRoute()
 	if len(opt121Routes) > 0 {
 		for _, r := range opt121Routes {
-			// Verify if nil before using the nil pointer.
-			if r.Dest != nil {
-				// set GW to nil for cloud based infrastructures with /32 host IPs 
-				routes = append(routes, &types.Route{Dst: *r.Dest, GW: nil})
+			route := &types.Route{Dst: *r.Dest, GW: r.Router}
+			// if router is not specified, add SCOPE_LINK so routes are installed
+			if r.Router.IsUnspecified() {
+				scopeLinkValue := int(netlink.SCOPE_LINK)
+				route.Scope = &scopeLinkValue
 			}
+			routes = append(routes, route)
 		}
 		return routes
 	}