Question about Null0 in route table

[10308140051]

i am analyzing the route to 10.105.16.95, user can access this ip from their pc.

so i tracert -d 10.105.16.95 from user pc:

here is the interface 10.105.32.17 in Router1

so i show ip route vrf XXX-RFD in Router1 to check the next-hop:

next-hop is 10.105.32.70, and the next-hop for 10.105.32.70 is Null0 in Router1 route table. so my question is how the packet send to 10.105.36.17? Null0 should drop all packet, right?

below is the configuration for interface 10.105.36.17 in Router2:

[nict]

Hi,

"next-hop is 10.105.32.70...." - Where do you get the IP from?

Did you show the full route table? I would assume you confuse 10.105.32.x with 10.105.36.x.

[10308140051]

destination ip 10.105.16.95 and next hop is 10.105.32.70, am i right?

[nict]

Yes, but you properly don't hit that entry. Please do as M02@rt37 mentions show ip route vrf XXX-RFD 10.105.32.70 on R1".

[M02@rt37]

Hello @10308140051 

Please do

#show ip route vrf XXX-RFD 10.105.32.70 on R1

[10308140051]

[10308140051]

i think 10.105.32.70 should use tunnel to Router2,before Null0. i am not very familiar with MPLS. but i think it is the reason. 

[MHM Cisco World]

show ip route vrf XXX-RFD 10.105.32.70 longest

share this 

MHM

[10308140051]

[MHM Cisco World · Accepted solution]

indeed there are two lookup 
one for prefix in RIB 
other for Label in MPLS label 

to be sure that packet use second lookup do 
debug mpls packet <<- then ping 
MHM

[paul driver]

Hello

---

@MHM Cisco World wrote:

indeed there are two lookup 
one for prefix in RIB 
other for Label in MPLS label 

to be sure that packet use second lookup do 
debug mpls packet <<- then ping 
MHM

---

Can you elaborate, the rtr isn't even running mpls by the looks of it?

[paul driver]

Hello
A Null route  can be used to negate possible network loops for packets sent to a network range(s) within it that are not being used so to save the rtr itself from trying to forward traffic it has no specific rib entry for

example:
rtr
int x/x
description LAN
10.105.16.1 255.255.255.0

int x/y
description WAN
X.X.X.1 255.255.255.252

ip route 0.0.0.0 0.0.0.0 X.X.X.2
ip route 10.105.0.0.0 255.255.0.0 Null0

As you can see the rtr has an active interface for 10.105.16.0/24  so any packet sent to that subnet will forwarded by the rtr however if a packet is sent to any other subset of that summary null route the rtr will NOT then forward it via its own default route.