Hi,
I’ve hit a bit of a challenge with the way that pppd creates the resolv.conf file.
Basically if you want to get dns servers from the other side you need ‘usepeerdns’ set.
If you set ‘usepeerdns’ then pppd will create resolve.conf (/etc/ppp/resolv.conf as standard, although changed in many dists)
The challenge is that if you have two pppd’s running, both getting DNS entries, then there is no way to specify a different file (so that you can be clever later) and the given file will be overwritten by the most recent connection. Also, with buiildroot builds the path is set to /etc/resolv.conf which causes even more of a problem since you can’t ‘usepeerdns’ without making your system use the provided resolvers.
It does feel wrong that just about every other aspect of pppd supports isolated multiple connections, but the resolv.conf file is a single path that will get overwritten by the last connection, and then, of course, if that connection drops the file is then incorrect!
Could I suggest a ‘noresolv’ config option that simply suppresses the creation of the resolve.conf file? It’s a very simple patch, has no compatibility issues with existing configuration and makes it possible to use ppp-up scripts to do the heavy lifting with no conflicting resolv.conf creations. This would also allow buildroot users to avoid the “forced use of peer dns”.
(The other option would be to have a configurable path for resolv.conf)
Cheers,
Lee.
diff -Naur pppd-orig/pppd/ipcp.c pppd-2.4.7/pppd/ipcp.c
--- pppd-orig/pppd/ipcp.c 2014-08-09 13:31:39.000000000 +0100
+++ pppd-2.4.7/pppd/ipcp.c 2015-01-26 07:27:04.758264172 +0000
@@ -91,6 +91,7 @@
static int default_route_set[NUM_PPP]; /* Have set up a default route */
static int proxy_arp_set[NUM_PPP]; /* Have created proxy arp entry */
static bool usepeerdns; /* Ask peer for DNS addrs */
+static bool noresolv; /* Don't write resolv.conf */
static int ipcp_is_up; /* have called np_up() */
static int ipcp_is_open; /* haven't called np_finished() */
static bool ask_for_local; /* request our address from peer */
@@ -209,6 +210,8 @@
{ "usepeerdns", o_bool, &usepeerdns,
"Ask peer for DNS address(es)", 1 },
+ { "noresolv", o_bool, &noresolv,
+ "disable creation of the resolv.conf file", 1 },
{ "netmask", o_special, (void *)setnetmask,
"set netmask", OPT_PRIO | OPT_A2STRVAL | OPT_STATIC, netmask_str },
@@ -1827,6 +1830,7 @@
script_setenv("DNS2", ip_ntoa(go->dnsaddr[1]), 0);
if (usepeerdns && (go->dnsaddr[0] || go->dnsaddr[1])) {
script_setenv("USEPEERDNS", "1", 0);
+ if (!noresolv)
create_resolv(go->dnsaddr[0], go->dnsaddr[1]);
}
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