I need security like that :

someone from the other network cannot enter on my network but my network can access his network.

You can use ACLs (Access-Lists) for that.

With routers at each side?

I have to build a link between 2 network. I'm gonna use 2 routers (one on each side). But, I need some security on that : I need to access the other network but the other network cannot access mine.

What kind of security I need for that? a security on router? with a software(firewall)? I don't know...

still not clear

if u ha s a private network no worry of hackin g from outside

if u r connecting to internet where u get a public address.save u r router fron denying telnet or use some good password

if u want to save u r data u can use data encryption like ipsec and so

wahy u go for a costly firewall and so

and if it is necassery for u to have a firewall u can have it on u r linux or other server

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