Routing Flashcards
is ECMP enabled by default?
NO!
what are the primary v4 and v6 routing tables?
inet.0 – v4 unicast
inet.1 – multicast forward cache
inet.2 – Multicast BGP (MBGP) for RPF checks
inet.3 – for MPLS path info
inet.4 – for Multicast source discovery routes
inet6.0 – v6 unicast
mpls.0 – mpls nexthops
Whats AD in Junos?
Route preference
What are the preferences for:
BGP, RIP, OSPF Internal, Direct, Static, Local, OSPF External?
Direct = 0
Local = 0
Static = 5
OSPF internal = 10
RIP = 100
OSPF AS External = 150
BGP = 170
Route preference… High or low preferred?
What’s the range?
low is best. 4.2 billion is highest (32bit int)
how do you see all routes for a given prefix in the RIB?
show route <prefix> exact</prefix>
Can you change route preference?
yes, but local and direct dont actually have any impact if you change em.
Default behaviour - how does ECMP work?
if there are two Equal cost routes to the same prefix, one path is picked at random.
This means where lots of prefixes are going across an equal cost link there is load distribution.
You can turn on per-flow ECMP.
how do you see route tables?
show route.
how do you see forwarding table?
show route forwarding-table
what happens if there is no match in the forwarding table?
packet hits the default FIB entry.
what are the two types in the FIB?
1st = Route type… dest (Destinations reachable), intf (local interfaces), perm (kernel installed things like multicast addresses, broadcast addresses), User (routes installed by a routing protocol or static config)
2nd = next hop type - broadcast, discard (silent), hold (pending resolution), local, multicast, multicast discard, recieve, reject, unicist, and load ballanced unicast.
In FIB, whats difference between DISCARD and REJECT?
DISCARD = drop quiet
REJECT = ICMP unreachable is sent
Whats a routing instance?
its basically VRF lite
Whats the default routing instance?
Master.
How do you set configure a routing instance type on a custom routing instance?
edit routing-instances <instance>
set instance-type</instance>
what are the routing instance types?
forwarding - for FBF for normal access layer applications
l2vpn - for l2vpn…
no-forwarding - used to split up huge networks
virtual-router - for non-VPN related application like virtualization
vpls - for point to multipoint VPN
vrf - for layer3 VPN
How do you create a routing instance?
edit routing-instance <name>
set instance-type <type>
set interface <interface>
set interface <interface>
set interface <interface>
set routing-options static route 0.0.0.0/0 next-hop x.x.x.x
set protocols ospf area 0.0.0.0 interface ge0/x/x
set protocols ospf area 0.0.0.0 interface ge0/y/y</interface></interface></interface></type></name>
where do you configure interfaces and routing protocols for routing instances?
inside the routing instance itself
how do you view routing instance tables?
show route table <routing>.routingtable</routing>
eg;
show route table vrf1.inet.0
how do you see interfaces in a given routing instance?
show interfaces terse routing-instance <name></name>
where do you configure a static route?
from edit routing-options!
what’s the equlivent of null0 for Junos?
bitbucket
whats the deal with static route next hops on junos?
static route next hops must by default be a connected interface.
No recursive lookups unless you enable it.
