EtherRake: Diagnosis and Monitoring in Data Center - PowerPoint PPT Presentation

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EtherRake: Diagnosis and Monitoring in Data Center

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* IP Router Errors ... the speed with which all devices on the network-having been notified of the failure-can calculate an alternate path ... DHCP DHCP problem ... – PowerPoint PPT presentation

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Title: EtherRake: Diagnosis and Monitoring in Data Center

1
EtherRake Diagnosis and Monitoring in Data
Center Enterprise Networks
Lab for Internet and Security Technology (LIST)
Northwestern Univ.
2
General Idea of EtherRake

Problem statement
Emerging DC and enterprise networks are mainly
comprised of large of switches which need
monitoring and diagnosis

3
General Idea of EtherRake

A centralized structure.
Collector at each switches
Collect Neighbors
Collect port information
Collect forwarding tables
Monitor Plane
Transmit collected information
Processing Center
Link the frames
Construct Logical Topology
Find the problems

4
Collector at each switches

Take Cisco switches for example
Port information
show port status (display interface ethernet0/1
for huawei)
Neighbor Information
show CDP neighbors
Forwarding tables (aka switch table)
show MAC interface mapping

5
Collector at each switches

Port information
Port Number 2 Bytes
Status 4 bits
Total 3 Bytes 100 300 Bytes lt 0.4KB per
switch
Neighbor Information
Mac Address 48 bits
Total 6Bytes 100 600 Bytes lt 0.6KB per switch
Forwarding Tables
To be decided. We are not using it in our
approach now. We can transfer updates only which
means normally we dont need to transfer
anything.
Total 1 KB 1024 (number of switches) 1MB in
one round.

6
Collector at each switches

Synchronization
Cristian's algorithm (P is processing center, and
S is a collector)
P requests the time from S
After receiving the request from P, S prepares a
response and appends the time T from its own
clock.
P then sets its time to be T RTT/2
Multiple measurement can reduce the error.
Accuracy. (T min) to (T RTT - min) where min
is the minimum one-way time.

7
Monitor Plane

Monitor Plane is a plane that co-exists with data
plane and control plane in the same channel. It
is used to transfer monitoring data.

8
Monitor Plane

Monitor plane is used to collect data for
monitoring data plane.
Switching in monitor plane has two methods.
Normally, control plane will assist monitor plane
forwarding.
Under error, monitor plane will do flooding.

9
Processing Center

Collect port information, forwarding tables and
neighbor information from all the switches.
Construct the logical topology of switches based
on the port neighbor info
Detect loops in the logical topology for STP loop
problems
Check for any missing/dead switches

10
Problems to Solve

STP Error Detection
End-to-end Error Detection
Other Hardware/Software Errors of Switches and
Their Detection
TRILL Potential Problems

11
End-to-end Connectivity Monitoring

Based on the neighbor and port information, check
if all switches and end hosts are on a connected
ST.
End hosts are also neighbors for leaf node
switch.
Forwarding table also records info of past
connectivity

12
Other Software Errors of Switches and its
Detection

One-Way Link Problem. No backward frames.
From EtherRakes view, interface of the other
direction is dead.
Deferred Frames. Buffer is full. Frames have to
be dropped.
Encode the buffer status (e.g., full) to the
status bit
Links between switches and routers
disabled/unactivated.
Detected by the port status bits or lack of
heartbeat
Switches down, e.g., unbootable IOS problems
Same as above

13
Limitations on Other Switch Software Errors
Detection

Some errors have to be detected at the data plane
or application plane.
VLAN Problems. Hosts in the same VLAN cannot
communicate with each other.

14
Hardware Errors of Switches and its Detection

Switch Port Errors.
Switch Module Errors.
Both will be detected by the port status reports

15
STP Errors (1)

Count to Infinity when removing the root

16
STP Errors (2)

Forwarding Loops
BPDU Loss Induced Forwarding Loops. If the
blocked port fails to receive BPDUs from its peer
bridge for an extended period of time, it may
start forwarding data.

17
STP Errors (3)

Forwarding Loops
MaxAge Induced Forwarding Loops (MaxAge 6)

18
STP Errors (4)

Forwarding Loops
Count to Infinity Induced Forwarding Loops
Pollution of Forwarding Tables

19
Previous STP Errors Detection

EtherFuse (sigcomm 07)
Plug a fuse into Ethernet
Problem Remaining
Where to plug it?
How many do we need?

20
Previous STP Errors Detection

Cisco Prevention Methods
Loop Guard. Prevent loss BPDU induced loops.

21
Some Existing Solutions

Cisco Discovery Protocol (CDP)
Discovery cisco apparatus in neighborhood
Monitoring aliveness of neighboring nodes
Limitations
No detail status report for diagnosis
Limited by one hop.
Cisco Unidirectional Link Detection (UDLD).
Detect One-Way Link Problem.

22
General Monitoring Metrics for Detection

Connectivity. Based on frames tree, EtherRake can
find the connectivity of a path.
Delay. EtherRake can link frames and calculate
the time spent on each switch.
Throughput. EtherRake can calculate throughput by
collected frames.

23
TRILL Potential Problems

Routing loops
Caused by inconsistent views of network topology.
Mitigated using hop count
Scalability issue
No clear idea on how much TRILL can scale

24
Backup
25
Detection of STP Errors by EtherRake

Find STP errors by EtherRake.
Link collected frames into traces
Detect frame forwarding loops
Leverage on the switch and ARP table info
Challenges
Scalability optimize collection of traces
Ambiguity and accuracy frame linking

26
End-to-end Connectivity Monitoring

Diagnose Connectivity Problem from A to B by
EtherRake
Find the frames that are on the way from A to B.
Link the frames and find a path.
Locate the problem.

27
IP Router Errors OSPF (1)

Network Convergence Time. The time taken by all
the OSPF routers in the network to go back to
steady state operations after there is a change
in the network state.

28
IP Router Errors OSPF (2)

Routing Load on Processors

29
IP Router Errors OSPF (3)

Route Flaps. Routing table changes in a router,
usually in response to a network failure or a
recovery.

30
Cisco Solution

Bi-directional Forwarding Detection (BFD)
Try to Speed Network Convergence (three parts).
Failure detection the speed with which a device
on the network can detect and react to a failure
of one of its own components, or the failure
of a component in a routing protocol peer.
Information dissemination the speed with which
the failure in the previous stage can be
communicated to other devices in the network
Repair the speed with which all devices on the
network-having been notified of the failure-can
calculate an alternate path through which
data can flow.

31
IP Router Errors DHCP

DHCP problem
Configuration problem.
Inability to acquire or renew a lease.
How to keep the same IP address in multi-boot
machines?

32
EtherFuse (1)

A Ethernet Fuse that is plugged into the network
for monitoring the status of network.

33
EtherFuse (2)

Detection of Count to Infinity
Detecting cost to the same root R of BPDUs

Detection of Forwarding Loops.
Combination of Passive Sniffing and Active
Probing.

35
Package View Switching

Forwarding packages from the view of packages.
Each package will have memory about the history
of the path it has already gone through and
decide which way to go based on the memory it
has.
Here is the steps. (Generally speaking, it is
deep-first searching from the view of packages.)

36
Package View Switching

Normally, when a package arrives at a switch, it
will choose the default port which is the port
that control plane provide.
If the package has already tried the default
port, it will randomly choose a new port that it
has never been to.
If the package tried every port at this switch,
it will go back to the port where it is from.
Package will be discarded when it arrived at its
origin and finds no other way to go. Or package
arrives at the destination which is the monitor
center.