In some areas, in India, you need to configure pppoe for BSNL
to connect to net.
docs.sun.com has a very good document
on this, but thought a quick guide to configure would be helpful.
So here is a quick quide to setup pppoe for BSNL networks.
(This is not restricted to BSNL, it should be applicable to any service which is based on pppoe.)

SUNW ppp packages should be already available for you unless you didn't install.If you didn't install you need the following packages.
Install them from your Solaris CD.

SUNWpppd - Solaris PPP Device Drivers.
SUNWpppdr - Solaris PPP configuration files.
SUNWpppdt - Solaris PPP Tunneling.
SUNWpppdu - Solaris PPP daemon and utilities.

There will be a file myisp.tmpl in /etc/ppp/peers directory.
copy it to file name bsnl
cp /etc/ppp/peers/myisp.tmpl /etc/ppp/peers/bsnl
edit bsnl file using you favorite editor. The uncommented section should look like
the following. where INTERFACE should be your ethernet interface name and
USERNAME is your broadband user name.

connect "/usr/bin/chat -f /etc/ppp/myisp-chat"  # dial into ISP.
sppptun
plugin pppoe.so
connect "/usr/lib/inet/pppoec INTERFACE"
user USERNAME           # my account name at my ISP
remotename bsnl # name of the ISP; for pap-secrets
noauth                  # do not authenticate the ISP's identity (client)
noipdefault             # assume no IP address; get it from ISP
defaultroute            # install default route; ISP is Internet gateway
updetach                # log errors and CONNECT string to invoker
noccp                   # ISP doesn't support free compression

Now there are 2 configuration files to update.
/etc/ppp/pap-secrets
/etc/ppp/chap-secrets
In these two files add the entry as follows

USERNAME        bsnl    PASSWORD

where USERNAME is your broadband username
and PASSWORD is you broadband password.

your configuration is done.

now run

#/usr/sbin/sppptun plumb pppoe INTERFACENAME
#/usr/sbin/sppptun plumb pppoed INTERFACENAME
#/usr/bin/pppd debug call bsnl

(debug is optional.)

you need to specify dns server to resolve dns names.
create a file in /etc with name resolve.conf
and copy the nameserver info.
for example:
echo nameserver  61.1.96.69 > /etc/resolv.conf

note: The ip specified here is bsnl nameserver,
         but might be different for you. Please ask your bsnl operator.
 dns file.
cp /etc/nsswitch.dns /etc/nsswitch.conf
Make a backup copy so that you can copy back when needed nexttime.
cp /etc/resolv.conf /etc/resolv.conf.bsnl

copy
In case you are still not able to resolv dns name.
check if dns/client service is running or not.
svcs -a | grep dns/client
if not enabled
svcadm enable dns/client
if not online, try starting
svcadm restart dns/client
or
svcadm refresh dns/client