Juniper first start selling core routers for ISPs, and expanded into edger data centers, wireless networking, networking for branch offices and other access and aggregation devices. Juniper is the third largest market-share holder overall for routers and switches used by ISPs.
So Juniper is used by ISP end because command can rollback to 50 times back and in juniper we can activate configuration for specific time being, this is major advantage of juniper device because we can’t know after committing of this command how device react.
Out of band vs In band
Out of band is used when we are unable to access the device through ssh or telnet then in this case we will use out of band management ip for accessing device 1. We can access the device 1 through connected other network device 2.
In band is used for direct communication of device through management ip. We can access device 1 through ssh or telnet.
Use of fxp port in juniper
1 There are 2 fxp interfaces in the router: fxp0 and fxp1
2 fxp1 is NOT for management, do not configure anything on fxp1
3 fxp0 is for out-of-band router management
4 fxp0 does not support VLAN tagging
5 fxp0 is not supported inside routing instance
6 fxp0 is not supported in Logical System
7 All router management protocols are supported through fxp0 (SNMP, NTP, SSH, Telnet, HTTP, HTTPS, etc).
8 Transit traffic through fxp0 is not supported
Means you cannot directly telnet/SSH from Your PC through Router1 fxp0 to Router2 lo0.0. You have to telnet/SSH to Router1 fxp0.0 and then initiate another telnet/SSH session from Router1 to Router2.
9 Firewall filter assigned to lo0.0 also filters traffic entering fxp0.0