[Dnsmasq-discuss] [PATCH] virtual dhcp range

[Sam]

Hi,
  here is a small patch that allows dnsmasq to assign IP addresses from
subnet, that is not configured on listening interface.

Use case:
  - I've a server(s) with multiple virtual machines, with network
settings configured via DHCP.
  - Each VM has statically assigned private IPs from subnet range on
the bridge, but some of them might have also public addresses from
subnet range that is *only routed* on that bridge.
  - With this patch I'm able to let dnsmasq assign this public
addresses by defining a *virtual subnet*. This is not otherwise allowed,
because dnsmasq is doing 'same net' checking on the incoming interface
subnet and to-be-assigned IP address.

Usage is simple:

dhcp-range=wan,XXX.XXX.XXX.1,*virtual*,255.255.255.240,12h

It's a quick hack, but it works for me perfectly.

Kind regards
  Sam



virtual-dhcp-range.diff


diff --git a/src/dhcp.c b/src/dhcp.c
index fb2f650..b9a73d0 100644
--- a/src/dhcp.c
+++ b/src/dhcp.c
@@ -526,8 +526,9 @@ static int complete_context(struct in_addr local, int if_index, char *label,
}

if (context->netmask.s_addr != 0 &&
- is_same_net(local, context->start, context->netmask) &&
- is_same_net(local, context->end, context->netmask))
+ ((is_same_net(local, context->start, context->netmask) &&
+ is_same_net(local, context->end, context->netmask)) ||
+ context->flags & CONTEXT_VIRTUAL))
{
/* link it onto the current chain if we've not seen it before */
if (if_index == param->ind && context->current == context)
diff --git a/src/dnsmasq.h b/src/dnsmasq.h
index 4b55bb5..95eee82 100644
--- a/src/dnsmasq.h
+++ b/src/dnsmasq.h
@@ -872,6 +872,7 @@ struct dhcp_context {
#define CONTEXT_OLD (1u<<16)
#define CONTEXT_V6 (1u<<17)
#define CONTEXT_RA_OFF_LINK (1u<<18)
+#define CONTEXT_VIRTUAL (1u<<19)

struct ping_result {
struct in_addr addr;
diff --git a/src/option.c b/src/option.c
index 50d26ba..af69e0e 100644
--- a/src/option.c
+++ b/src/option.c
@@ -2775,6 +2775,8 @@ static int one_opt(int option, char *arg, char *errstr, char *gen_err, int comma
new->flags |= CONTEXT_STATIC;
else if (strcmp(a[1], "proxy") == 0)
new->flags |= CONTEXT_PROXY;
+ else if (strcmp(a[1], "virtual") == 0)
+ new->flags |= CONTEXT_STATIC | CONTEXT_VIRTUAL;
else if (!inet_pton(AF_INET, a[1], &new->end))
ret_err(_("bad dhcp-range"));