What is the reason the IS-IS adjacency fails?

user@R1> show
interfaces {
ge-1/1/0 {
unit 0 {
family inet {
address 10.100.1.1/30;
}

family iso;
}
}
lo0 {
unit 0 {
family inet {
address 10.100.10.1/32;
}
family iso {
address 49.1001.0010.0100.00;
} } }
}
protocols {
isis {
level 1 disable;
interface ge-1/1/0.0 {
level 2 disable;
}
interface lo0.0;
}
}
user@R2> show
interfaces {
ge-1/1/0 {

unit 0 {
family inet {
address 10.100.1.2/30;
}
family iso {
mtu 1496;
} }
}
lo0 {
unit 0 {
family inet {
address 10.100.10.2/32;
}
family iso {
address 49.1002.0010.0200.00;
} } }
}
protocols {
isis {
interface ge-1/1/0.0 {
level 2 disable;
}
interface lo0.0;
}

}

Click the Exhibit button.
Referring to the exhibit, R1 and R2 are directly connected using interface ge-1/1/0.
What is the reason the IS-IS adjacency fails?

user@R1> show
interfaces {
ge-1/1/0 {
unit 0 {
family inet {
address 10.100.1.1/30;
}

family iso;
}
}
lo0 {
unit 0 {
family inet {
address 10.100.10.1/32;
}
family iso {
address 49.1001.0010.0100.00;
} } }
}
protocols {
isis {
level 1 disable;
interface ge-1/1/0.0 {
level 2 disable;
}
interface lo0.0;
}
}
user@R2> show
interfaces {
ge-1/1/0 {

unit 0 {
family inet {
address 10.100.1.2/30;
}
family iso {
mtu 1496;
} }
}
lo0 {
unit 0 {
family inet {
address 10.100.10.2/32;
}
family iso {
address 49.1002.0010.0200.00;
} } }
}
protocols {
isis {
interface ge-1/1/0.0 {
level 2 disable;
}
interface lo0.0;
}

}

Click the Exhibit button.
Referring to the exhibit, R1 and R2 are directly connected using interface ge-1/1/0.
What is the reason the IS-IS adjacency fails?

A.
R2 has an MTU value of 1496 configured on ge-1/1/0.

B.
R2 and R1 have different area IDs.

C.
R1 is configured for Level 2, and R2 is configured for Level 1.

D.
R1 is configured for both Level 1 and Level 2 to be disabled.

Explanation:

Show Hint

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Oliv

Oliv

The response can-t be B.
Many mistake on this one :
Look at the MTU = 1496.
For IS-IS to work you should have a Maximum MTU of 1492.
The second point is that there is on R1 :
protocols {
isis {
level 1 disable;
interface ge-1/1/0.0 {
level 2 disable;
}

It meen’s that the interface can’t talk level 1 and level 2.
So here there is an issue with the number of answer.
The response is A and D.

Reply

uno76

uno76

For ISIS to work mtu must be at least 1492, so right answer is D

Reply

Anon

Anon

ISIS will establish over MTUs Larger than 1492 this is the minimum MTU size. There isn’t a Maximum MTU required. Core routers run with MTU size of 9134 on the ISIS interfaces and 9117 for ISIS:

lab-r1> show interfaces xe-0/3/0
Physical interface: xe-0/3/0, Enabled, Physical link is Up
Interface index: 178, SNMP ifIndex: 1801
Link-level type: Ethernet, MTU: 9134, LAN-PHY mode, Speed: 10Gbps, BPDU Error: None, Loopback: None, Source filtering: Disabled,
Protocol iso, MTU: 9117

lab-r1> show isis adjacency
Interface System L State Hold (secs) SNPA
xe-0/3/0.0 lab-r2 2 Up 24

On router 1 ISIS level 1 is disabled globally and Level 2 is disabled under the interface this is why ISIS will not establish.

Therfore D is correct.

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