Configuring DMVPN with ZBF (Hub and Spoke Topology)

Document

Mar 26, 2011 7:37 PM
Mar 26th, 2011

Objective:

To configure ZBF on both  a DMVPN  hub and a DMVPN spoke router.

Problem Description:

DMVPN(hub and spoke deployment) is a hub-and-spoke deployment model in which the primary enterprise resources are located in a large central site, with a number of smaller sites or branch offices connected directly to the central site over a VPN.

Zone Based Firewall is an advanced configuration model for the Cisco IOS Firewall feature set. It offers intuitive policies for multiple-interface routers, increased granularity of firewall policy application, and a default deny-all policy that prohibits traffic between firewall security zones until an explicit policy is applied to allow desirable traffic.

Often in case of small remote sites the DMVPN router serves not only as the GRE and Crypto aggregation router but also as the network edge device. In such cases, users often prefer to add an extra layer of security by enabling Zone Based Firewall feature set on the router. Network location of the crypto headend in relation to the headend firewall(s) impacts both the accessibility and performance of both systems. The network manager must ensure that all firewalls are properly configured to allow the tunnel traffic bi-directionally. The crypto headend must be accessible to the branch router because all crypto sessions are initiated by the branch router.

Prerequisites:

  1. DMVPN Design guide
  2. Basic DMVPN configuration guide
  3. ZBF Design and Application guide

Please note, only single tiered headened architecture is discussed in this document. In case of double tiered architecture, ZBF needs to be configured to allow GRE traffic on one router and IPSEC traffic on the other.

Scenario:

DMVPN with ZBF.png

Solution:

One of the biggest differences between CBAC and ZBF is in the manner in which the firewall policies are applied.  In CBAC the inspection policies are defined per interface, however to improve granularity and flexibility in the firewall configuration, ZBF was modelled based on zones. Each interface is made part of a zone, and the inspection policies are applied between two zones. Usually the private networks are part of the in-zone, and the poblic networks are part of the out-zone. All traffic destined to any ip address on the router itself is part of the "self" zone. By default traffic from any zone to the self zone is permitted, however if there is a specifc out-self zone then special care needs to be taken to permit those kinds of traffic that will be destined to the router itself. Depending on the crypto and DMVPN headend or branch placements, the following protocols and ports are required to be allowed:

UDP Port 500—ISAKMP as source and destination

UDP Port 4500—NAT-T as a destination

IP Protocol 50—ESP

IP Protocol 51—AH (if AH is implemented)

IP Protocol 47—GRE

Routing protocol

Please note, only single tiered headened architecture is discussed in this document. In case of double tiered architecture, ZBF needs to be configured to allow GRE traffic on one router and IPSEC traffic on the other.

Please keep in mind that the above considerations need to be made in additition to the configuration reqiured to allow normal traffic as desired.

There are various ways that routers can be configured. I have identified 4 such use cases base on what zone each interface is mapped to:

Use of 2 zones

interface

  zone   
insideinternal
outsideexternal

tunnel

external*

*it is not recommended to configure the tunnel interface in the same zone as the inside interface, because in this case, the DMVPN traffic does not require any kind of zone pair configuration at all to allow the traffic to pass through, thus making the FW completely redundant as far as the DMVPN traffic is concerned.

Use of 3 zones

interface   zone  
insideinternal
outsideexternal
tunnel

dmvpn

For both the above use cases you can refer to the document Using VPN with Zone-Based-Firewall for the configuration guide.

Use of self zone

In this particular use case the interfaces can be configured using either 3 or 2 zone as described above, however an additional self zone is also applied in the zone pair configuration to provide added protection against traffic sent to the router.

Configuration:

The following configuration example is for the case where:

1. the hub is configured with 2 zones along with a self zone

2. the spoke is configured with 3 zones along with a self zone

Configuration on Hub:

crypto isakmp policy 1

     encr 3des

     hash md5

     authentication pre-share

     group 2

crypto isakmp key cisco123 address 0.0.0.0 0.0.0.0

!

crypto ipsec transform-set dmvpn-trans esp-3des esp-md5-hmac

     mode transport

!

crypto ipsec profile dmvpn-pro

     set transform-set dmvpn-trans

!

class-map type inspect match-any self-out-class

     match protocol icmp

class-map type inspect match-any self-out-dmvpn-class

                    match access-group name test

                    match protocol isakmp

class-map type inspect match-any int-ext-class

     match protocol telnet

     match protocol ssh

     match protocol icmp

!

policy-map type inspect int-ext-policy

     class type inspect int-ext-class

          inspect

     class class-default

          drop

policy-map type inspect self-out-policy

     class type inspect self-out-dmvpn-class

       pass

     class type inspect self-out-class

       inspect

     class class-default

       drop

!

zone security internal

zone security external

zone-pair security int-ext source internal destination external

     service-policy type inspect int-ext-policy

zone-pair security ext-int source external destination internal

     service-policy type inspect int-ext-policy

zone-pair security self-ext source self destination external

     service-policy type inspect self-out-policy

zone-pair security ext-self source external destination self

     service-policy type inspect self-out-policy

!

interface Tunnel1

     ip address 172.16.1.1 255.255.255.0

     no ip redirects

     ip mtu 1400

     ip nhrp authentication cisco123

     ip nhrp map multicast dynamic

     ip nhrp network-id 1

     ip nhrp holdtime 600

     zone-member security external

     no ip split-horizon eigrp 1

     tunnel source Ethernet0/1

     tunnel mode gre multipoint

     tunnel key 10000

     tunnel protection ipsec profile dmvpn-pro

!

interface Ethernet0/0

     ip address 192.168.1.1 255.255.255.0

     zone-member security internal

!

interface Ethernet0/1

     ip address 1.1.1.1 255.255.255.0

     zone-member security external

!

router eigrp 1

     network 192.168.1.0 0.0.0.255

     network 172.16.1.0 0.0.0.255

     auto-summary

!

ip forward-protocol nd

ip route 0.0.0.0 0.0.0.0 1.1.1.2

!

ip access-list extended test

     permit gre any any

     permit esp any any

     permit eigrp any any

Configuration on Spoke:

crypto isakmp policy 1

     encr 3des

     hash md5

     authentication pre-share

     group 2

crypto isakmp key cisco123 address 0.0.0.0 0.0.0.0

!

crypto ipsec transform-set dmvpn-trans esp-3des esp-md5-hmac

     mode transport

!

crypto ipsec profile dmvpn-pro

     set transform-set dmvpn-trans

!

class-map type inspect match-any int-ext-clas

     match protocol telnet

     match protocol ssh

     match protocol icmp

class-map type inspect match-any self-ext-class

     match protocol icmp

class-map type inspect match-any self-ext-dmvpn-class

     match protocol isakmp

     match access-group name test-dmvpn

class-map type inspect match-any dmvpn-ext-class

     match protocol icmp

!

policy-map type inspect dmvpn-ext-policy

     class type inspect dmvpn-ext-class

       inspect

     class class-default

       drop

policy-map type inspect int-ext-policy

     class type inspect int-ext-clas

       inspect

     class class-default

       drop

policy-map type inspect self-ext-policy

     class type inspect self-ext-class

       inspect

     class type inspect self-ext-dmvpn-class

       pass

     class class-default

       drop

!

zone security internal

zone security external

zone security dmvpn

zone-pair security int-dmvpn source internal destination dmvpn

     service-policy type inspect int-ext-policy

zone-pair security dmvpn-int source dmvpn destination internal

     service-policy type inspect int-ext-policy

zone-pair security int-ext source internal destination external

     service-policy type inspect int-ext-policy

zone-pair security ext-int source external destination internal

     service-policy type inspect int-ext-policy

zone-pair security self-ext source self destination external

     service-policy type inspect self-ext-policy

zone-pair security ext-self source external destination self

     service-policy type inspect self-ext-policy

!

interface Tunnel1

     ip address 172.16.1.2 255.255.255.0

     ip mtu 1400

     ip nhrp authentication cisco123

     ip nhrp map multicast 1.1.1.1

     ip nhrp map 172.16.1.1 1.1.1.1

     ip nhrp network-id 1

     ip nhrp holdtime 600

     ip nhrp nhs 172.16.1.1

     zone-member security dmvpn

     no ip split-horizon eigrp 1

     tunnel source Ethernet0/1

     tunnel destination 1.1.1.1

     tunnel key 10000

     tunnel protection ipsec profile dmvpn-pro

!

interface Ethernet0/0

     ip address 192.168.2.1 255.255.255.0

     zone-member security internal

!

interface Ethernet0/1

     ip address 2.2.2.1 255.255.255.0

     zone-member security external!

ip access-list extended test-dmvpn

     permit esp any any

     permit gre any any

     permit eigrp any any

Known Caveats:

  1. CSCtn65512 - ZBF drops DMVPN traffic post IPSec decryption when using shared TP
  2. CSCta00183 - ZBF: Adding ins for esp from out to self zone may break DMVPN and EIGRP

Suggested Reading:

  1. DMVPN with CBAC configuration
  2. Using VPN with Zone-Based Firewall
  3. Anyconnect on IOS with ZBF


Average Rating: 5 (1 ratings)

Comments

walter baziuk Sat, 10/01/2011 - 09:38

thank you for the posting

that is what i was looking for

i addition, my requirements also need NAT and

a means to ensure all SPOKE traffic only goes to the HUB

I am required to have the HUB acts as the inet gateway

even though most of my spokes will connect over the inet, their traffic needs to be "tunneled" to the HUB

some SPOKE sites are on the corporate network, they will be treated the same.

This ensures that we can moinitor and control inet traffic without having to replicate the strong filtering and monitoring at all SPOKE sites

any tips or advice? for the later two addional requirements?

atbasu Mon, 11/28/2011 - 07:01 (reply to walter baziuk)

Walter, to control the traffic from the spokes so that they only go to the hub before they go anywhere else, you just need to control the routing. For example if you are using EIGRP then removing then enabling next-hop-self instead of disabling it should fix this issue for you. As far as NAT is concerned, just treat the tunnel interface like any other interface for natting, it should work.

martin.smid Thu, 11/24/2011 - 02:42

Hi,

pretty nice guide. I have got few questions though. We are using separate ACLs for self-out and out-self zone pairs. in out_to_self ACL we have allowed gre any any but not in self_to_out ACL and the tunnel works fine. Also we did not permit eigrp any any (in both ACLs) and the neighbours come up with no problem. Could you provide some insight into this? I

atbasu Mon, 11/28/2011 - 06:54 (reply to martin.smid)

Martin, I would need to take a look at the configuraiton that you have could you post it here?

martin.smid Mon, 11/28/2011 - 07:42

Hi,

The physical interface is in outside, while the Tunnel interfaces are in zone "DMVPN". There is no eigrp protocol in either of the ACLs and GRE is allowed only in OUT->Self. I have changed the ACLs so they are mirrored. The EIGRP neighbour is up over 5 days now on both Hub and Spoke, the traffic flows fine, I can telnet and ping the destinations I need.

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