initRouteTable() code question

[zhao-wuji-ahh]

Hi,Why the api named initRouteTable() but the api mainly deal with joining the default groups.Is it necessary make the line (routing_table = NULL) in the api? It makes me confused.
void initRouteTable(void) {
unsigned Ix;
struct IfDesc *Dp;

// Clear routing table...
routing_table = NULL;

// Join the all routers group on downstream vifs...
for ( Ix = 0; (Dp = getIfByIx(Ix)); Ix++ ) {
    // If this is a downstream vif, we should join the All routers group...
    if( Dp->InAdr.s_addr && ! (Dp->Flags & IFF_LOOPBACK) && Dp->state == IF_STATE_DOWNSTREAM) {
        my_log(LOG_DEBUG, 0, "Joining all-routers group %s on vif %s",
                     inetFmt(allrouters_group,s1),inetFmt(Dp->InAdr.s_addr,s2));

        k_join(Dp, allrouters_group);

        my_log(LOG_DEBUG, 0, "Joining all igmpv3 multicast routers group %s on vif %s",
                     inetFmt(alligmp3_group,s1),inetFmt(Dp->InAdr.s_addr,s2));
        k_join(Dp, alligmp3_group);
    }
}

}