In Juniper devices, an access-internal route is a special kind of static route used to represent a directly connected subscriber. It's a /32 route (meaning a single IP address) with a preference of 12, which is higher than regular static routes.

When DHCP is configured, the router automatically adds an access-internal default route pointing to the DHCP server as the next hop. This helps the DHCP server communicate with connected subscribers by making sure traffic is routed correctly.

However, in some situations—like when the router is acting as a DHCP relay agent—you might not want this default route to be added automatically. See in the example below where access internal route gets installed even though it has not been been configured explicitly.

root@SRX> show route table inet.0

inet.0: 178 destinations, 266 routes (178 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

0.0.0.0/0 *[Access-internal/12] 5d 03:31:27, metric2 0 
> to 10.10.10.1 via dl0.0

While there is a workaround to suppress the default route learned through DHCP (See this article: Preventing DHCP from Installing Access, Access-Internal, and Destination Routes by Default  to get more information), there is no direct workaround to suppress the default route learned via the dialer interface (dl0) on SRX. 

Possible workaround: If the intention is for the BGP-learned default route to take precedence over the access-internal route, we can configure a policy to lower the AD value of the BGP default route as follows:

set policy-options policy-statement test term 1 from protocol bgp

set policy-options policy-statement test term 1 from route-filter 0.0.0.0/0 exact

set policy-options policy-statement test term 1 then preference subtract 164

set policy-options policy-statement test term 1 then accept

set policy-options policy-statement test term 2 then accept

The above configuration will make the AD value for BGP learned default route to 6.

For more information on AD value and route information you can refer to this article: Understanding Route Preference Values (Administrative Distance)