24 Jan

BGP Route Server on ASR1000

BGP Route Server is feature designated mostly for IX (Internet Exchange) deployment. You can find many deployment around the world mostly using open software like Quagga, but it’s also available on Cisco’s ASR1000 routers. Route server is an advanced route reflector which provide customized policy support for each service provider, which means that standard path selection can be overridden by route policies set per particular provider.
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10 Aug

Deleting a subinterface that has IPv6 EIGRP running on it and crashing IOS XE

In some cases router running IOS XE might crash or produce traceback if we try to delete logical interface (like ie. port-channel) or subinterface that runs IPv6 EIGRP. This can occur mostly on XNE or older releaseses, has been fixed in new ones. Cisco have internal bug CSCtd63242 describing this problem (might be released into public).
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23 Jul

BGP Unknown path error on ASR1000

In some situations you can see following error message while trying to establish BGP neighborship

%BGP_SESSION-5-ADJCHANGE: neighbor IPv4 Unicast topology base removed from session  Unknown path error

This can be misconfiguration or internal bug described (or rather just mentioned because I’d say bug description is almost empty) in CSCsy10339 bug ticket if you are using release prior to 12.2(33)XNE. If this is misconfiguration you’d rather expect error message like

%BGP_SESSION-5-ADJCHANGE: neighbor IPv4 Unicast topology base removed from session  Peer closed the session

. This can be quite confusing and leads to looking for problem elsewhere than it exists.

12 Apr

Passing username in CUBE-SP

By default when register message passes SBC username in contact field is replaced with random string. This string identifies pinhole opened for particular user for management purposes. But this behavior is not always desirable. Many SIP implementations identifies user by Contact field and rewriting it with random string would prevent application from registration.
SBC can be configured to pass username set in Contact field. To do this you have to configure

    registration contact username passthrough

This have to be set on adjacency that should not rewrite username when SIP REGISTER comes from

30 Mar

ASR1k NAT really does not like secondary addresses

Cisco routers never liked secondary addresses if NAT is configured on same interface. You can always expect unpredictable behaviors, and making translations over secondary addresses never worked. On ASR1k it’s even worse.

Configuration for testing was pretty simple.

interface TenGigabitEthernet0/2/0
 ip address secondary
 ip address
 ip nat outside
ip nat pool test-robot netmask
ip nat inside source list test-r-list pool test-r overload

On ISR this configuration should work, at least I made it run on dynamips and 12.4T software. On ASR1k and IOS XE it’s not working regardless of version of software used. If you enable debugging you’ll find something like that in logs

*Mar 24 06:49:12.482: NAT: setup alias for (redundancy_name , idb TenGigabitEthernet0/2/0, flags 0x2)
*Mar 24 06:49:12.482: NAT: installing alias for address, addr_flags 0x2
*Mar 24 06:49:12.482: NAT: alias insert failed for

Traffic flows through ASR router, translation entry is created in NAT table and it reaches destination, but almost every traffic that is sent back and should use same translation is dropped by ASR. Almost every because ICMP pings are working fine, UDP and TCP flows are dropped.

There are two solutions of this problem. You can create translation rule using interface instead of pool, then ASR will use primary address as a source of translation and it will work fine.

ip nat inside source list test-r-list interface TenGigabitEthernet0/2/0 overload

Other solution is to split physical interface into two subinterfaces using dot1q tagging and use ip nat outsideonly on subinterface with public addresses.

What’s also disturbing is fact, that NetFlow Event Logger (refer to this post, that should send NetFlow v9 events to collector starts sending weird data. In my tests it stopped sending informations about creation or removal of NAT entry. No data sets were sent to collector, just templates that weren’t the ones described by templateId=259.

23 Mar

Missess counters on Cisco routers

According to Cisco’s documentation misses represents “number of times the software performs a translation table lookup and fails to find an entry, and creates one“. So all routers should have some misses in their counters. Let’s look at some 1841 router statistics:

C1841#sh ip nat statistics 
Total active translations: 3339 (0 static, 3339 dynamic; 3339 extended)
Peak translations: 8114, occurred 18:35:17 ago
Outside interfaces:
Inside interfaces: 
Hits: 28658670  Misses: 0

No misses, only hits that increases every time “the software performs a translation table lookup and finds an entry“. It works same on every ISR and 7200 routers. But still documentation says otherwise.
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21 Mar

NetFlow Event Logger on ASR1k

ISP’s are not ready yet to deploy IPv6 to end customers and lack of IPv4 address spaces force them to use NAT in their networks. Unfortunately more and more governments require logging what users do and what IP addresses they are connecting to. NAT even logger to syslog is available for quite long time already. But with all AJAX and P2P applications logging, and especially querying logged data is ineffective. On ASR1k routers you can log NAT and firewall events using NetFlow v9.
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15 Mar

Testing SSO on ASR1k

IOS XE on ASR1000 provides two forms of redundancy. First one is well-known hardware redundancy available in ASR1006 where two RP’s and ESP’s can be installed. On other platforms software redundancy and ISSU can be configured. Because IOS XE is in fact just one of a Linux processes running on the platform while system is booting up no one but two instances of iosd are executed in background, but only one is active. Both processes are running on same Route Processor. Standby IOS process can be switched to in the event of an IOS failure, and can also be used to upgrade sub-package software in some scenarios as the standby IOS process in an ISSU upgrade.
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