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
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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
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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
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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
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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.
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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.
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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.
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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.
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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
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Problems to Solve
- STP Error Detection
- End-to-end Error Detection
- Other Hardware/Software Errors of Switches and
Their Detection - TRILL Potential Problems
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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
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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
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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.
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Hardware Errors of Switches and its Detection
- Switch Port Errors.
- Switch Module Errors.
- Both will be detected by the port status reports
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STP Errors (1)
- Count to Infinity when removing the root
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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.
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STP Errors (3)
- Forwarding Loops
- MaxAge Induced Forwarding Loops (MaxAge 6)
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STP Errors (4)
- Forwarding Loops
- Count to Infinity Induced Forwarding Loops
- Pollution of Forwarding Tables
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Previous STP Errors Detection
- EtherFuse (sigcomm 07)
- Plug a fuse into Ethernet
- Problem Remaining
- Where to plug it?
- How many do we need?
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Previous STP Errors Detection
- Cisco Prevention Methods
- Loop Guard. Prevent loss BPDU induced loops.
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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.
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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
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Backup
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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
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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.
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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.
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IP Router Errors OSPF (2)
- Routing Load on Processors
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IP Router Errors OSPF (3)
- Route Flaps. Routing table changes in a router,
usually in response to a network failure or a
recovery.
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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.
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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?
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EtherFuse (1)
- A Ethernet Fuse that is plugged into the network
for monitoring the status of network.
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EtherFuse (2)
- Detection of Count to Infinity
- Detecting cost to the same root R of BPDUs
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- Detection of Forwarding Loops.
- Combination of Passive Sniffing and Active
Probing.
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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.
