JNCIS-ENT · domain
Tunnels
This domain covers Junos tunnel interfaces: IP-IP, GRE, and related encapsulation used to carry traffic across a transport network. Questions test the tunnel interface's role with routing protocols, outer-header protocol numbers, which interface family to configure for the encapsulated payload, and the operational commands that display configured tunnel source and destination addresses.
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What to know about Tunnels
Be able to configure and verify Junos tunnel interfaces, including GRE and IP-IP. Know that the interface family reflects the encapsulated payload, not the transport, and use the correct operational command to confirm tunnel source and destination addresses.
The primary function of a Junos tunnel interface when used with routing protocols
The protocol number in the outer IP header for an IP-IP tunnel
Which interface family must be configured under a gr- interface unit for GRE over IPv4 carrying IPv6
The operational command that shows configured tunnel source and destination addresses
Watch out for
Common Tunnels exam traps
- ▸Assuming the tunnel interface's family must match the transport network rather than the encapsulated payload being carried.
- ▸Confusing the outer IP header protocol number for IP-IP with GRE or other encapsulation protocol numbers.
- ▸Believing a tunnel interface forwards or routes traffic on its own instead of relying on routing protocols and the underlying transport.
Question index
All Tunnels questions (36)
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Which TWO factors must be carefully managed when running OSPF over a GRE tunnel interface on Junos devices? (Choose two.)
Hard2An administrator configures a GRE tunnel with a tunnel key enabled for security segmentation between two sites. The tunnel comes up, but traffic fails to pass. Debugging reveals that packets are dropped because the receiving router rejects the packets. What is the most probable configuration mismatch?
Hard3You are configuring a GRE tunnel over an IPv4 network, but you want to secure the GRE traffic using IPsec (GRE over IPsec). In Junos, how is this typically structured on SRX or MX devices?
Hard4On an MX Series router, you configure a GRE tunnel that terminates on a routing instance (VRF). Where must the tunnel source and destination addresses be routable?
Hard5Which TWO parameters are mandatory when configuring a basic GRE tunnel interface in Junos? (Choose two)
Easy6When configuring an IP-IP tunnel on Junos, can you run multicast routing protocols like PIM over the IP-IP tunnel?
Hard7You are configuring a GRE tunnel carrying IPv6 traffic over an IPv4 transport network (GRE over IPv4). Which interface family must be configured under the gr- interface unit?
Hard8Which THREE characteristics distinguish GRE tunnels from IP-IP tunnels on Junos devices? (Choose three)
Medium9You need to configure an IP-IP tunnel on a Junos device. Which interface prefix is designated for IP-IP tunnels in the Junos CLI?
Medium10You have configured an IP-IP tunnel, but traffic fails to pass through. You run 'show interfaces ip-0/0/0' and see that the output displays 'Input drops' incrementing rapidly. What is the most likely reason?
Medium11You are configuring an IP-IP tunnel on a Junos routing platform. Which statement correctly identifies how IP-IP encapsulation differs from GRE encapsulation?
Medium12An administrator has configured a GRE tunnel between two SRX Series devices. Traffic originating from behind the local security zone destined for the tunnel interface is being dropped by default security policies. Which action must be taken to ensure transit traffic can enter the GRE tunnel?
Hard13Which protocol number is used in the outer IP header for an IP-IP tunnel?
Easy14You are configuring a GRE tunnel and want to ensure that integrity checks are performed on the transmitted packets to detect corruption. Which parameter should you add to the tunnel configuration?
Medium15Which THREE factors should be considered when planning MTU size for traffic traversing a GRE tunnel? (Choose three)
Medium16An administrator notices that CPU utilization on the Routing Engine spikes when a high volume of transit traffic is directed through a locally terminated GRE tunnel on an MX router without inline services configured. What is the cause?
Hard17Which Junos operational mode command is used to verify the operational status and packet statistics of configured GRE tunnel interfaces?
Easy18An administrator needs to configure a basic GRE tunnel between two Junos devices across a routed IP network. Which interface family must be enabled on the physical transit interface to allow the GRE encapsulated packets to traverse the network?
Easy19Which TWO statements are true regarding Junos tunnel interface naming conventions? (Choose two)
Easy20When troubleshooting a non-functional GRE tunnel on a Junos device, which TWO operational commands or verification steps are most effective for diagnosing the root cause? (Choose two)
Hard21When configuring a GRE tunnel on Junos, which two parameters are mandatory under the specific gr- interface hierarchy to establish the tunnel endpoint connectivity?
Easy22Which TWO tools or commands can be used on Junos to verify the operational packet flow through a tunnel interface? (Choose two)
Easy23Which TWO actions must be performed when configuring a functional GRE tunnel between two Junos devices over an intermediate IP network? (Choose two.)
Hard24You have configured a GRE tunnel, and you want to verify that the tunnel source and destination parameters match what is expected. Which command shows the configured tunnel source and destination addresses?
Medium25Which THREE statements regarding IP-IP tunnels on Junos devices are accurate? (Choose three)
Medium26When configuring an IP-IP tunnel on a Junos device, what happens to the source and destination IP addresses of the original packet when it is encapsulated?
Hard27Which interface naming convention is used by Junos OS to identify a generic routing encapsulation (GRE) tunnel interface?
Easy28Which THREE statements are true regarding IP-IP encapsulation in Junos OS? (Choose three.)
Medium29What is the primary function of a Junos tunnel interface when used in conjunction with routing protocols?
Easy30You are configuring a GRE tunnel between two Juniper routers to carry OSPF traffic. The tunnel is up, but OSPF adjacencies are not forming. Which two actions would you take to troubleshoot and resolve this issue? (Choose two.)
Hard31You are configuring a GRE tunnel between two Juniper routers. The tunnel interface is gr-0/0/0, and you have configured the tunnel source as ge-0/0/0.0 and the tunnel destination as 192.0.2.2. You notice that the tunnel interface is up, but traffic sent through the tunnel is being dropped. Which action would you take to resolve this issue?
Medium32Which Junos configuration statement defines the destination address of a GRE tunnel?
Easy33You configure a GRE tunnel between two routers. Router A can ping Router B's tunnel IP address successfully, but devices behind Router A cannot ping devices behind Router B across the tunnel. What is the most likely cause?
Medium34An enterprise network uses a GRE tunnel to connect two sites running OSPF. OSPF neighbor adjacencies fail to form over the GRE tunnel even though unicast pings between the tunnel endpoints succeed. Upon inspecting interface configurations, you notice that OSPF hellos are not being received by the peer. What is the most likely cause of this issue?
Hard35What is the official protocol number assigned in the outer IP header for GRE encapsulation?
Easy36When configuring a GRE tunnel source and destination address on a Junos device, which configuration hierarchy is used?
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Frequently asked questions
- What does the Tunnels domain cover on the JNCIS-ENT exam?
- Be able to configure and verify Junos tunnel interfaces, including GRE and IP-IP. Know that the interface family reflects the encapsulated payload, not the transport, and use the correct operational command to confirm tunnel source and destination addresses.
- How many questions are in this domain?
- This page lists all 36 Tunnels questions in the JNCIS-ENT question bank. The actual exam draws from this domain proportionally to its weighting in the official exam blueprint.
- What is the best way to practise this domain?
- Start with a short focused session (10 questions) to identify gaps, then work through explanations. Repeat with a longer session once the weak areas feel solid.
- Can I practise only Tunnels questions?
- Yes — the session launcher on this page filters questions to this domain only. Choose any session length for inline explanations and scoring.